The melting point of the stone in degrees. Forgotten ancient technology - the ability to soften stones. Temperature and features of the diamond melting process
RenegadePizzaGuy
Can stone be "recycled" by melting and cooling it? [closed]
This is what I've been thinking about for a while.
Let's say a marble block is used to sculpt a statue. Most of the stone has broken off and is practically useless. Instead of throwing it, maybe it will melt back into bricks?
I am asking this because it will probably require a lot of power and heat. I'm also not sure if the melting and cooling process will change the material, such as making it more brittle.
Edit: To clarify, I don't mean marble specifically. I want to know what is usually required to melt the stone, if the cooling process will affect it and if it would be practical at all to do
Raditz_35
Are you asking if it is possible to melt stone and cool it again, are you asking specifically about marble, are you asking if it makes economic sense, are you asking if it is good for the environment, are you asking how certain types of stones are made? geologically? I can think of a dozen more interpretations for your question, maybe you should be more specific
Andrew Dodds
Marble being calcium carbonate is the only example that will NOT work.
AlexP
Rock chips are also useful. And there is no economic reason to recycle stone - after all, the Earth is a huge chunk of stone... On the other hand, recycling stone is exactly what the cycle of stone does; it will take a very long time.
@AlexP Glass is made from a material that is abundant in the earth's crust; yet we are recycling it.
AlexP
@Kaz: "Made from"! = "Yes". Table salt is made from chlorine (a poisonous gas) and sodium (a metal that reacts violently with water). To make glass out of sand, we use an enormous amount of energy; it makes sense to avoid this again and again when we can reuse glass.
Answers
Andrew Dodds
It depends on your stone.
Breeds such as granite, with large crystal sizes, are the result of VERY slow cooling and crystallization. So while in theory you could melt down and recrystallize this type of stone, it would probably take you hundreds or thousands of years to do so.
Basalt, a fine-grained igneous rock, would be fine. It would still take quite a long time to settle down.
Obsidian and volcanic glass would be very easy - by definition, it cools quickly when it erupts. There are no problems with disposal, except for the necessary heat.
Now problems..
Sandstone(and other sedimentary rocks) - you couldn't melt them and reshape them, obviously. You can grind them down to a grain of sand, THEN try to press them together with the appropriate cement (silica or carbonate, depending on the original stone). It will take pressure and quite a bit of time.
Slate Now, you not only have to grind it up, but also lightly recrystallize it under several hundred degrees of pressure, with more pressure in the direction normal to the splitting. For a long time.
Marble Marble cannot be melted under surface pressure, it decomposes into calcium oxide and CO2. If you had a very high pressure crucible and a means to heat it, you could melt the marble and recrystallize it.
blueschist It's getting a little more difficult. You need a pressure equivalent to about 20 km of rock and a temperature of about 400 degrees Celsius.
eclogite A type of metamorphic rock of very high quality. 45 km deep and c. 700 degrees C. For many years to get the crystal size.
So...unless you want volcanic goggles to work with them, it would probably be a lot easier to just buy some more. Rock formation takes a long time, and usually under conditions of high temperature and pressure, which are not cheap to reproduce.
kingledion
Great answer. You should point out the general difference between igneous rocks (for which melting will work by definition, although as you mentioned, cooling times vary) and other rock types.
expressed in numbers
Could you add an estimate of how long "long" is? At the moment I don't know if it's months and therefore not commercially viable, or if we're talking centuries where we most likely won't live to see the result.
MSalters
@nwp: Considering we're definitely not running out of rock anytime soon, even one hour wouldn't be commercially viable. Marble would be the main exception, and it's not exactly stone.
PlasmaHH
For many stones, these processes can produce similar in composition and physical properties, but not in appearance. Especially for marble, the streaks of impurities make it so beautiful that it takes one more extra step to paste them.
Andrew Dodds
@nwp - It depends mainly on the size of the crystal, and hence the uncertainty. The largest crystals can take years, thousands of years to form, depending on how long the granite takes to cool.
Willk
Here is the opportunity to link my all-time favorite episode "How It's Made: Stone wool insulation». It is precisely melted and processed rock, which is made commercially.
The idea was inspired by "Pele's hair" that actually exists in Hawaii: molten basalt whipped into thin, hair-like strands. In the video, they show the making of artificial lava from crushed basalt (and slag), which is then beaten into wool and made into mats. Quality goods.
However, most stones will melt at around 1500 degrees Celsius (2750 Fahrenheit), the previous company says they do it at 1520º C. Therefore, it is quite difficult and requires advanced technology.
POJO-boy
Iron melts at 1538 °C. Since cast iron has been used in cookware for at least two thousand years, the practice of melting and cooling sufficiently large quantities of materials at this temperature cannot be considered "high tech"—it may date back to the late age of iron.
Alberto Yagos
Cast iron melts at 1200ºC. Blast furnaces did not appear in Europe until the 13th century.
POJO-boy
Thanks for correction. Cast iron has a lower melting point than pure iron. The 13th century for the blast furnace is late medieval and early renaissance technology, so it is still not considered cutting edge technology.
ruakh
@pojo-guy: "Advanced technology" doesn't necessarily mean what you think; It's easy to find examples on Google that use terms like "metalworking", "pottery", "astronomy", "shipbuilding", "horseback riding", and "wheel". (I don't actually quite understand what that means; I don't think it's a completely nonsensical phrase, but it's still probably too vague to be terribly useful in this answer.)
ChrisW
Speaking of marble, yes - historically people fed old architectural marble (like ancient Roman marble) in a lime kiln: to make mortar and concrete ("lime" is a key ingredient in cement, mortar, concrete)
Feeding marble in kiln
Why did the population begin to feed the sculptural and architectural elements of marble, which, as elsewhere, once adorned public monuments and elite mansions in the Galilee, to neighboring likini? The main reason given by scholars for this reuse of marble is that it happened for economic reasons. As mentioned earlier, marble is superior to limestone when it comes to lime production. While this is true, for much of antiquity, marble was considered too rare and valuable to be used for this purpose, and was instead used mainly for purposes of decoration and lavish display. When liquin kilns began to be built within the city by late antiquity, scholars concluded that this was because by that time marble was fairly available in the form of architectural decorations and sculptures. In addition to the superior quality of the marble, the reuse of this stone from former city structures also likely saved significant transportation costs. Then, according to these scholars, the burning of sculptural and architectural marble in the lime kilns installed in cities during Late Antiquity was primarily chosen for its productive efficiency: the product was superior and transportation more cost-effective.
So this particular type of "rock" doesn't need very advanced technology... they did it in the real world, in ancient times.
Draco18s
This is not really an answer to the question. The question is to see if they can make stone from scraps of rock by melting and dissolving it (in the example of marble) to get a new material for modeling. This is an answer to the question of whether scrap metal can be specifically used for other industrial uses other than sculpture.
ChrisW
The OP asked if marble could be turned into bricks. Other answers have suggested that it is difficult; while this answer assumes that something similar has been done in the real world using vintage technology, so maybe this answer does add something and was worth it.
great duck
It fails to answer the question. The OP wants to know if marble can be melted down and turned into marble.
David Richerby
@ChrisW No, he turns the stone chips into mortar: bricks are made from clay. And I commented as a direct response to your comment. (Also, I love that people who downvote without explanation get "Downwater, please explain" comments, while those who explain get hit with "Well, you could just downvote.")
ivanivan
There are, of course, other ways to reuse, unuse, or repurpose things.
The shards can be ground/ground very finely and then used to be mixed with some other substance to give strength (like making cement or making metal filings in something like JB Weld) or making other crafts (sandpaper is very good) ground stone/mineral of various types glued to paper)
And, of course, only small pieces of stone-drainage systems can always be used, as part of a large natural water filter, paving, etc.
However, on a relatively small scale - like those remnants that were after Michelangelo carved his David - it would not provide significant enough remnants of economies of scale to make and do anything, but leave large chunks for smaller jobs. or training, etc., or throwing small pieces down the French sewer.
Martin Bonner
In fact, in the case of marble, I suspect that Michelangelo's waste would have been burned for lime - marble makes high quality quicklime, but is usually too valuable for that.
The well-known "tabletop" sells its visitors that the mountains of Iran, Turkey and Greece are " marble melted by the bombardment of the VCC - the great space civilization".
Photos of travels in Iran, Turkey and Greece are interesting there, but it seems that there are no chemists there.
I also treat chemistry with respect from afar, but, now, there are big doubts about the "melting of marble mountains".
But many things are not clear how they are done, omitting the brackets melting marble.
# Behistun_Inscription
silicon lava
Most characteristic of the volcanoes of the Pacific ring of fire. Usually very viscous and sometimes freezes in the mouth of the volcano before the end of the eruption, thereby stopping it. A plugged volcano may swell somewhat, and then the eruption resumes, as a rule, with a strong explosion. The average flow rate of such lava is several meters per day, and the temperature is 800–900 °C. It contains 53-62% silicon dioxide (silica). If its content reaches 65%, then the lava becomes very viscous and slow. The color of hot lava is dark or black-red. Solidified silicic lavas can form black volcanic glass. Such glass is obtained when the melt cools quickly, without having time to
The formation of marble is the result of the so-called metamorphism process: under the influence of certain physical and chemical conditions, the structure of limestone (sedimentary rock of organic origin) changes, and as a result, marble is born.
In construction practice, "marble" is called metamorphic rocks of medium hardness, which take polishing ( marble, marbled limestone , dense dolomite, carbonate breccias and carbonate conglomerates).
Until now, the word `marble` refers to different breeds that are similar to each other. Builders call marble any durable limestone that can be polished. Sometimes a similar breed is mistaken for marble serpentinite. True marble on a light break resembles sugar.
About the extraction of marble in Iran, yes, they mine:
We are pleased to introduce our corporation "Omarani Yazdbaf" is a well-known stone mining corporation. Our company mines onyx (light green, white), marble (cream, orange, red, pink, yellow) and travertine (chocolate, brown
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In general, nothing is clear - who climbed the mountain and why he knocked out a relief in the mountain.
Everyone knows that a volcanic eruption is a terrible natural phenomenon. Lava carries away thousands of people, absorbs all life, turning it into ashes. It's almost impossible to run away from her. Melting stone allows you to get lava at home!
youtubeTherefore, it is not recommended to build housing near volcanoes. Even if they are extinct, they can come to life at any moment and then trouble will not be avoided. But people do not look at the warnings of hydrometeorological centers and continue to build up empty places.
Lava is a red-hot mass, viscous in appearance, which appears from stones of a silicate composition under the influence of enormous temperatures and erupts from volcanoes.
The King of Random channel decided to show its subscribers how to turn ordinary stones into lava at home. For these purposes, they used a smelter and the latest technology.
The guys from the channel received a letter. They appreciated the idea and decided to bring it to life. Random kings are not afraid of difficulties and are ready to take on any challenge.
The King of Random suggested two ways to turn rocks into lava. The first method was to heat the natural material in a furnace, and the second was to heat the stone with the help of external influence of a special device resembling a welding machine.
As a result of the first method, the stones melted, but quickly became hard and brittle. But with the second method, the guys managed to achieve the desired result. The melting temperature of the stones is different. It depends on their chemical nature.
Watch an interesting and informative video! You've definitely never seen anything like this before! Captivating video. Enjoy watching and have a nice day!
Here is your current upbringing, - Yanechek said instructively. - And if you sometimes say something to your son, he answers: “You, dad, don’t understand this, now other times, another era ... After all, bone weapons, he says, are not yet the last word: one day the material.” Well, you know, this is too much: has anyone ever seen a material stronger than stone, wood or bone! Although you are a stupid woman, you must admit: that ... that ... well, that this goes beyond all boundaries.
Karel Chapek. On the decline of morals (from the collection "Apocrypha")
Now we are simply not able to imagine our life without metals. We are so accustomed to them that at least subconsciously we resist - and in this we are like the hero of the prehistoric era quoted above - any attempts to replace metals with something new, more profitable. We are well aware of the difficulty in some industries with lighter, more durable, and cheaper materials. A habit is an iron corset, but even if it were made of plastic, it would still be more convenient. However, we have skipped a couple of millennia. The first consumers of the metal did not even suspect that future generations would put their discovery on a par with the most outstanding milestones in the path of economic and technological development - with the advent of agriculture and with the industrial revolution of the 19th century.
The discovery probably took place - as it sometimes happens - as a result of some kind of unsuccessful operation. Well, for example, like this: a prehistoric farmer needed to replenish his stock of stone plates and axes. From the heap of blanks that lay at his feet, he selected stone after stone and with skillful movements beat off one plate after another. And then some kind of shiny angular stone fell into his hands, from which, no matter how much he hit it, not a single plate was separated. Moreover, the more diligently he beat this shapeless piece of raw material, the more it began to look like a cake, which in the end could be crushed, twisted, stretched and twisted into the most amazing shapes. So people first got acquainted with the properties of non-ferrous metals - copper, gold, silver, electron. In the manufacture of the first, very simple jewelry, weapons and tools, they had enough of the most common technique of the Stone Age - a blow. But these objects were soft, easily broken and blunted. In this form, they could not threaten the dominance of the stone. And besides, metals in their pure form, amenable to stone processing in a cold state, are extremely rare in nature. And yet they liked the new stone, so they experimented with it, combined processing techniques, set up experiments, and thought. They had, of course, to endure many failures, and a very long time passed before they succeeded in discovering the truth. At high temperatures (the consequences of which they knew well from the firing of ceramics), the stone (which we today call copper) turned into a fluid substance that took the form of any form. Tools could acquire a very sharp cutting edge, which, moreover, could be sharpened. The broken tool did not have to be thrown away - it was enough to melt it and cast it again in the form. Then they came to the discovery that copper can be obtained by roasting various ores, which are much more common and in greater volume than pure metals. Of course, they did not recognize the metal hidden in the ore at first sight, but these fossils undoubtedly attracted them with their colorful color. And when, after a long series of random, and subsequently conscious quantitative experiments, was added the discovery of bronze - a solid golden alloy of copper and tin, the dominance of stone, which lasted millions of years, was shaken at its very foundation.
In Central Europe, copper products first appeared in isolated cases at the end of the Neolithic, they were somewhat more common in the Eneolithic. However, even earlier, in the seventh - fifth millennium BC. e., the more developed Near East began to obtain copper by smelting suitable for this purpose oxide (cuprite), carbonate (malachite), and later sulfide ores (copper pyrites). The simplest was the smelting of oxide ores obtained from weathered copper deposits. Such ores can be at a temperature of 700–800 degrees. restore to pure copper:
Cu 2 O + CO → 2Cu+CO 2
When ancient casters added tin to this product (think of the Egyptian recipe), an alloy arose that far surpassed copper in its properties. Already half a percent of tin increases the hardness of the alloy four times, 10 percent - eight times. At the same time, the melting point of bronze decreases, for example, at 13 percent tin by almost 300 °C. The gates to a new era have opened! Behind them we will no longer meet that old homogeneous society, where everyone did almost everything. The manufacture of a metal object was preceded by a long way - the search for ore deposits, the extraction of ore, smelting in melting pits or furnaces, pouring into molds; all this required a whole complex of special knowledge and skills. Therefore, among the artisans, differentiation begins according to specialties: miners, metallurgists, foundry workers, and, finally, merchants, whose occupation is necessary for the rest and therefore highly valued by them. Not everyone could successfully engage in the whole complex of such complex activities. Modern experimenters also encountered many failures and difficulties when they tried to repeat some of the technological methods of prehistoric metallurgists and foundry workers.
Sergey Semenov discovered by trace method and experimentally confirmed the fact that at the dawn of the Bronze Age people used very crude stone tools made of granite, diorite and diabase in the form of hoes, clubs, anvils and crushers for mining and crushing ores.
Experimenters tested the smelting of malachite ore in a small deepened hearth without the use of air blast. They dried the horn and overlaid it with stone slabs in such a way that a round embrasure appeared with an inner diameter of about one meter. From the charcoal used as fuel, a cone-shaped structure was made in the forge, in the middle of which ore was placed. After several hours of burning, when the temperature of the open flame reached 600–700 °C, malachite melted to the state of oxide copper, that is, metallic copper was not formed. A similar result was achieved in the next attempt, when cuprite was used instead of malachite. The reason for the failure was, in all likelihood, an excess of air in the forge. A new test with malachite covered with an inverted ceramic vessel (the whole process proceeded in the same way as in the previous cases) resulted in sponge-like copper. Experimenters obtained a small amount of solid copper only when malachite ore was crushed before smelting. Similar experiments were carried out in Austria, whose Alpine ores were of great importance for prehistoric Europe. However, the experimenters pumped air into the furnace, thanks to which they reached a temperature of 1100 ° C, which reduced oxides to metallic copper.
In one of the experiments, the experimenters used to cast a bronze sickle half of the original stone mold, which was preserved from the finds near Lake Zurich, to which they made a paired side. Both mold parts were dried at 150°C and bronze was cast at 1150°C. The mold remained intact, the casting was good. Then they decided to try out a bronze double-leaf ax mold found in France. It was thoroughly dried at 150°C. Then it was poured with bronze at a temperature of 1150 °C. An excellent quality product was received. At the same time, not the slightest damage was found on the bronze mold, which was the most important result of the experiment. The fact is that before the experiment, some researchers expressed the opinion that the hot metal, in all likelihood, will combine with the mold material.
In the production of objects of a more complex configuration, the ancient casters used the technique of casting with the loss of a casting mold. They coated the wax model with clay. When the clay was fired, the wax flowed out, and then it was replaced by bronze. However, when taking out a bronze casting, the molds had to be broken, so there was no need to count on its reuse. The experimenters practiced this method based on the 16th century technological instructions for the manufacture of gold and silver bells. During experiments, they replaced gold with copper in order to simultaneously test the possibility of replacing precious metals with ordinary ones. The melting point of gold is 1063 °C, copper - 1083 °C. As a sample, a casting of a copper bell from the site of the first millennium BC was chosen. e. The mold was made from a mixture of clay and charcoal, and the model was made from beeswax. A small core was made from a mixture of clay and ground charcoal, and a small pebble was placed in it - the heart of a bell. Wax was applied around the core with a thin layer equal to the wall thickness of the future casting, and a wax ring was stuck to form the pendant of the future bell. A handle-shaped wax boss was attached over the ring in such a way that it served as a hopper for the molten metal during pouring, solidification and shrinkage of the metal in the casting. A hole was cut in the wax shell on the bottom of the bell, so that the shaping mixture of clay, charcoal and wax filled the hole and fixed the position of the core after melting the wax model and during casting. The wrapped form was pierced at the top with several straws, which were later either burned or simply removed. Hot air escaped from the mold during casting through the holes. The whole model was covered with several layers of ground clay and charcoal and dried for two days. Then it was again covered with a layer of coal and clay (for the strength of the mold) and a funnel-shaped pouring hopper from the same shaping mixture was attached above the boss. The boss was attached slightly obliquely so that the mold was cast in an inclined state. This was to ensure the unimpeded flow of the molten broom along the lower part of its front side, while on the opposite side there should have been an outflow of air displaced by the metal until the entire mold was completely filled with molten metal. Before smelting, fragments of copper ore were thrown into a bunker closed with a lid. After drying, the mold was placed in an oven equipped with a draft channel. The furnace was filled with four and a half kilograms of charcoal and heated to a temperature of 1200 °C. The wax model and the wax boss melted and evaporated, the copper melted and glassed into a mold, where it formed a metal bell. Then the outer "shirt" was broken, the metal boss was removed, and the clay core, which formed the hollow part of the bell, was dug out - only a pebble remained.
Arthur Pitch conducted a whole series of experiments dedicated to the embossing of bronze: wire, spiral, sheet, solid ring and shaped rod. The experience gained was used by him in the manufacture of replicas of bronze twisted rings of the Durin culture, dating back to the early Iron Age. In total, he made seventeen replicas, each of which was provided with a description of the archaeological original, a list of tools and devices used, an analysis of the material composition, and, finally, an explanation of individual operations and an indication of the duration of the technological process. Least of all time was spent on replica number two - twelve hours. The longest - sixty hours - demanded replica number fourteen.
During the Bronze Age, the inconveniences associated with production began to gradually come to light, primarily the limited availability of raw materials in nature and the depletion of deposits known by that time. This, of course, was one of the reasons why people were looking for a new metal that could meet the ever-increasing needs. Iron met these requirements. At first, his fate resembled the fate of copper. The first iron, meteoric origin, or obtained by accident, appeared already in the third and second millennia BC. e. in the Eastern Mediterranean. More than three thousand years ago, metallurgical furnaces began to operate in Western Asia, Anatolia and Greece. They appeared with us in the Hallstatt era, but finally took root only in the La Tène era.
Among the raw materials used in the ancient iron-smelting business (oxides, carbonates, silicates). The most common were oxides: hematite, or iron luster, limonite, or brown iron ore, a mixture of iron hydroxides, and magnetite, which is very difficult to restore.
The reduction of iron begins already at approximately 500 °C. You are probably now asking why iron came into use centuries or millennia later than copper and bronze. This is due to the conditions of its then production. At the temperatures reached by the first metallurgists in their hearths and furnaces (about 1100 °C), iron never passed into a liquid state (at least 1500 °C is required for this), but accumulated in the form of a pasty mass, which, under favorable conditions, was welded into a crucible impregnated with slag and residues of combustible materials. With this technology, a negligible amount of carbon passed into iron from charcoal - about one percent, so it was soft and malleable even in a cold state. Products from such iron did not reach the hardness of bronze. The points were easily bent and quickly blunted. This was the so-called direct, immediate production of iron. It persisted until the 17th century. True, in some prehistoric and early medieval furnaces it was possible to obtain iron with a higher level of carbon content, that is, a kind of steel. Only from the 17th century, furnaces began to be used, where iron was produced in a liquid state and with a high carbon content, that is, hard and brittle, from which an ingot was cast. To obtain steel, it was necessary to make high-carbon iron malleable by removing some of the carbon it contained. Therefore, this method is called indirect iron production. But even prehistoric blacksmiths expanded their experience through experiments. They found that by heating iron in a forge, when the temperature from charcoal reached 800–900 °C, they could produce products with much better properties. The fact is that a thin layer with a higher carbon content is formed on their surface, which gives the object the quality of low-carbon steel. The hardness of iron increased when the principle of hardening was discovered and its advantages began to be used.
Probably the earliest experiment in the study of ancient metallurgy was ordered to be carried out about a hundred years ago by Count Wurmbrand. Its metallurgical workers used charcoal, burnt ore in the simplest furnace with a diameter of one and a half meters and, in the process of smelting, improved combustion conditions by weak air injection. After twenty-six hours, they obtained approximately twenty percent yield of iron, from which various objects were forged. Relatively recently, English experimenters also carried out the smelting of iron ore in a similar device. They reconstructed a simple smelting furnace in the likeness of a furnace found at an ancient Roman site. The original forge had a diameter of 120 cm and a depth of 45 cm. Before smelting, the British researchers burned the ore in an oxidizing environment at a temperature of 800 °C. After lighting the charcoal, new layers of ore and charcoal were gradually added to the hearth. During the experiment, artificial blasting with a tuyere was used. It took about four hours for one layer of ore reduced with carbon monoxide to penetrate into the hearth. The operating temperature reached 1100 °C, and iron accumulated near the mouth of the lance. The output during the melting process was 20 percent. From 1.8 kg of ore, 0.34 kg of iron was obtained.
Gilles' experiments in 1957 opened a series of experiments on the reduction of ore in various types of shaft furnaces. Already in the first experiments, Joseph Wilhelm Gilles proved that a prehistoric shaft-type furnace could work successfully using the natural movement of air on leeward slopes. During one of the tests, he recorded a temperature of 1280 to 1420 ° C in the center of the furnace, and 250 ° C in the space of the grate. The result of the melts is 17.4 kg of iron, that is, 11.5 percent: the charge consisted of 152 kg of brown iron ore and iron sheen and 207 kg of charcoal.
Many experimental melts in replica stoves of the Roman era were carried out in Denmark, especially in Lejre. It turned out that one successful smelting can produce 15 kg of iron. For this, the Danes had to use 132 kg of swamp ore and 150 kg of charcoal, which was obtained by burning one cubic meter. m hardwood. The melting lasted about 24 hours.
Systematic experiments are being carried out in Poland in connection with the study of an extensive iron-working area discovered in the Swietokrzyskie Mountains. Its heyday belongs to the late Roman era (from the third to the fourth century AD). Only from 1955 to 1966, archaeologists explored 95 metallurgical complexes with more than 4 thousand iron-smelting furnaces in the Świętokrzyskie mountains. Archaeologist Kazmezh Belenin believes that the total number of such complexes in this area is 4,000 with 300,000 ovens. The volume of their production could reach 4 thousand tons of iron of market quality. This is a huge figure that has no analogues in the prehistoric world.
The origins of the mentioned iron-smelting industry date back to the Late Late (last century BC) and the early Roman period, when metallurgical complexes with ten or twenty furnaces were located directly in the center of the settlement. Their products satisfied only local, very limited needs. Starting from the middle Roman period, the production of iron began to be of an organized nature, it reached its greatest rise in the 3rd-4th centuries. The furnaces were located in the form of two rectangular compartments, separated by a drift for the attendants. In each of the sections of the furnace, two, three, and even four were grouped. Thus, several dozen ovens were located in one complex, but settlements with a hundred or even two hundred ovens were not some rare exceptions. The hypothesis about the existence of iron exports during this period is confirmed not only by the number of metallurgical furnaces with high productivity, but also by numerous finds of treasures with thousands of Roman coins. In the era of the Great Migration of Nations and in the early Middle Ages, production again fell to a level that met local needs.
A prerequisite for the emergence of such mass metallurgical production in the Roman era was sufficient reserves of wood and ore. Metallurgists used brown iron ore, hematite, and iron spar. They mined some ores using the usual mining method, as evidenced, for example, by the Staszic mine with a system of shafts, adits and with the remains of supports and tools dating back to the Roman era. However, they did not disdain marsh ore either. Furnaces with a deep hearth and an elevated shaft were used, which had to be broken when extracting an iron sponge (crown).
Since 1956, experiments have been carried out in the Świętokrzyskie mountains that reconstruct the production process: ore mining on fires (to remove moisture, enrich and partially burn harmful impurities, such as sulfur); obtaining charcoal by charcoal burning in piles; building a furnace and drying its walls; ignition of the furnace and direct melting; development of a mine shaft and excavation of an iron goblet; forging an iron goblet.
In 1960, at one of the most famous sites (Nova Sbupya), the Museum of Ancient Metallurgy was opened, near which, every year since 1967, in September, the technology of prehistoric metallurgy has been demonstrated to the general public. Such a demonstration begins with the delivery of ore from the mine to the metallurgical complex, in which iron-smelting furnaces are located at different levels. Here the ore is crushed by hammers and dried. Drying and beneficiation of ore take place in roasting facilities. Such a device has the form of a stack formed by layers of firewood, shifted by ore. The stack is set on fire simultaneously from all sides. After combustion, the dried, roasted and enriched ore is piled up, from where it is taken for loading. In the vicinity of the complex there is also a workplace for coal miners, which shows the production of charcoal - laying and erecting a pile, burning, dismantling a pile, transporting coal to an open storage, grinding and, finally, use in a kiln. This is followed by heating the furnace, installation and laying of the bellows. The staff of the complex consists of ten workers - miners, metallurgists, coal miners and auxiliary workers who are smelting and at the same time preparing the second furnace for the experiment. Melting continues with the removal of an iron sponge from the hearth, and the shaft must first be broken.
In 1960, Polish and Czech specialists joined forces and began to jointly conduct metallurgical experiments. They built two recovery furnaces based on Roman era models. One was an analogue of the type of stove from the Sventokrzyskie mountains, the second corresponded to an archaeological find in Lodenice (Czech Republic). For smelting, hematite ore and beech coal were used in the proportion of one to one and a half and one to one and weak air blast. Air flow, temperature and reducing gases were systematically controlled and measured. During an experiment on an analogue of the Polish furnace, which had a deepened hearth and different shaft superstructures - 13, 27 and 43 cm high, scientists found that the smelting process was concentrated at the necks of both opposite tuyeres, where mobile slag and sponge iron were formed (from 13 to 23 percent of iron and only about one percent of metallic iron in drops in the composition of the lower slag). The temperature near the lances reached 1220–1240°C.
The process proceeded in a similar way during the experiments in the Lodenitz furnace; only the appearance of the slag and iron formations was different. The temperature near the tuyere was 1360°C. And in this replica, an iron cry was obtained with traces of carburization. The iron goblet was always formed at the necks of the lances, while the lighter slag flowed through its pores into the bottom onto the charcoal layer. Efficiency in both cases did not exceed 17-20 percent.
Further experiments were aimed at clarifying the level of Slavic metallurgical production of the 8th century, the remains of which were preserved in the complexes discovered in Želechovice near Uničov in Moravia. It was primarily about determining whether it was possible to produce steel in such furnaces. As for the yield of iron and the efficiency of the furnace, this was of secondary interest, since the numerous measurements carried out during the experiment adversely affected the smelting process.
Zhelechovitsky type ovens are wonderful devices of ingenious design. Their shape made it possible to carry out high-quality filling by filling. Experiments have shown that metallurgists could produce charcoal themselves during smelting. The fuel had to be put into the furnace in small portions, otherwise there was a danger of blocking the narrow shaft hole close to the bottom of the furnace. Low-melting iron ores had an indisputable advantage, but zhelechovitsky-type furnaces were able to reduce both hematites and magnetites. The preliminary roasting of the ore was not difficult and was, in all probability, advantageous in any case. The centimeter size of the ore pieces was optimal.
The filling formed a melting cone in the hearth of the furnace, and the material subsequently filled up was then automatically transported to the cavity behind the tuyere, where the epicenter of the sting was formed in which the product was protected from reoxidation by forced air.
An important parameter is the volume of air injected into the furnace. If there is not enough blowing, the temperature is too low. A larger volume of air leads to a significant loss of iron, passing into the slag. The optimal volume of blown air was 250–280 liters per minute for the Želechovitsky furnace.
Experimenters further discovered that, under certain conditions, high-carbon steel can be obtained even in primitive separate furnaces and, therefore, there is no need for subsequent carburization. During experiments at the Želechovitsky complex, archaeologists noted the fact that all furnaces were equipped with a sink behind the tuyere. They hypothetically took this space as a chamber for heating and carburizing the bloom, which accumulated there immediately after melting. They tested the stated hypothesis in a replica of the Želechovitsky furnace. After smelting hematite ore from coal for six hours, the kritsu was heated in a reducing environment in the rear cavity of the furnace. The temperature in the chamber was 1300 °C. The product was removed from the oven at a red-white heat. The slag flowed through the pores of the spongy iron mass. The product contained carburized iron along with pure iron.
During the Novgorod archaeological expedition in 1961 and 1962, experimental iron smelting was carried out in a replica of an ancient Russian above-ground shaft furnace of the 10th–13th centuries, well known both from archaeological and ethnographic sources. Taking into account the fact that the drying of the oven from clay - namely, from which the originals were made - would be delayed for several weeks, the experimenters used clay blocks in its manufacture. The gaps between them were filled with a lubricant of clay and sand. The interior of the ovens was smeared with approximately a centimeter layer of clay and sand. The furnace had a cylindrical shape with a diameter of 105 cm and a height of 80 cm. A sixty-centimeter blast furnace was placed in the center of the cylinder. The diameter of the upper hole was 20 cm, the hearth - 30 cm. In the lower part of the furnace, the experimenters made a hole 25x20 cm in size, which served to inject air and release slag. The control of the regime inside the furnace was carried out through two diopters in the wall, through which parts of the measuring equipment were introduced. The blowing was carried out by the latest method - an electric motor, the power of which was brought into line with the parameters achieved by bellows. The twenty centimeter lance was again a replica of the old type, made from a mixture of clay and sand. The oven dried for three days under normal weather conditions.
For smelting, they used mostly swamp ore with a very high iron content (about 77 percent), and in two cases also supergene ore, which was crushed to the size of a walnut. Before filling, the ore was dried, and some of it was burned on fire for about half an hour. Melting began with heating the furnace with dry pine logs with natural draft for two hours. Then the house was cleaned and covered with a thin layer of coal dust and crushed coal. This was followed by the installation of a lance and coating all the cracks with clay. Blowing started when the shaft was completely filled with charcoal through the smoke hole. After five or ten minutes, the pine coal flared up, and in half an hour a third of it burned down. The empty space formed in the upper part of the mine was filled with a charge consisting of coal and ore. When the mixture settled, another portion was added to the resulting void. A total of seventeen experimental heats were carried out.
From the charge, which consisted of 7 kg of ore and 6 kg of charcoal, 1.4 kg of sponge iron (20 percent) and 2.55 kg of slag (36.5 percent) were obtained. The mass of charcoal in none of the heats did not exceed the mass of ore. Melts carried out at elevated temperatures produced a smaller volume of iron. The fact is that at higher temperatures, a greater amount of iron passed into the slag. In addition to the temperature regime, the accuracy of choosing the optimal moment for the release of slag had a serious impact on the quality and efficiency of melting. With too early or, conversely, too late release, the slag absorbed iron oxides, and this led to a lower output. With a high content of iron oxides, the slag became viscous and therefore flowed out worse and got rid of sponge iron.
The significance of the Novgorod experiments is especially great because during some of them it was possible to release slag. Melting lasted from 90 to 120 minutes. In this type of furnace, it was possible to process up to 25 kg of ore in one cycle and get more than 5 kg of iron. The reduced spongy iron was deposited not directly at the bottom of the furnace, but somewhat higher. Obtaining metallic cast iron from this product was a further independent and complex operation associated with new heating. And these experiments confirmed the hypothesis that in conventional reduction furnaces, under certain conditions, iron is carburized, that is, raw steel is obtained. In reduction furnaces, where the process proceeded without slag discharge, a conglomerate was obtained, which consisted of sponge iron (upper part), slag (lower part) and coal residues. The separation of sponge iron from slag was usually carried out mechanically.
Recently, archaeologists have discovered in the Moravian Kras, near the town of Blansko, many traces of ancient metallurgical activity - hearths of furnaces, fragments, walls, lances, lumps - dated back to the 10th century. In a model of one of the pocket hearth furnaces, an experiment was carried out which showed that carburized steel could also be produced in such a device and that sponge iron was sintered at the level of the tuyere and therefore could not be detected under the slag ingots.
