Chapter Eight. [Evenstad 1790:437-440]
About the re-smelting of bloomery- or crude iron, in the forge, to make finer iron.
Iron which has only been transformed from ore to crude iron in the bloomery, is ill suited for any practical purpose whatsoever, even if it is of the very best kind; it may well be wrought and worked into crude tools, but when it breaks, it is impossible to weld back together. It retains a number of impurities, which have to be expelled before the iron is perfected, and this can be achieved by re-smelting in the forge.
Many, even experts, when they see bloomery iron of the best sort, have difficulty judging whether it has been re-smelted or not; thus great frauds can be perpetrated with such iron. However a very certain distinctive feature is that the iron is blackish and dark when it has only been smelted in the bloomery, while it is bluish after it has been re-smelted. And this re-smelting is done in the following manner. From the forge all impurities are cleared out, including charcoal-remnants, in such a way that the cavity is one inch deep under the pipe (the tuyère), but it must not be deeper; for it must be possible for the draught to reach the iron in the cavity, to cool it, otherwise one obtains steel instead of iron. The cavity is made 11 to 12 inches long from the side of the tuyère and about 10 inches broad. It is pounded compact, flat, and level at the bottom, so that it does not incline to any side. The bellows and the tuyère must be placed in such a way that the draught goes precisely forward, neither up, down, nor to either side.
The forge is filled with a pile of charcoal, and when it is burning well, a half or a whole bloom of iron is laid upon it. As soon as the iron lump is so hot that it casts sparks it is grasped with tongs and held close over the airblast from the tuyère, whereafter it melts and falls down into the forge. While the lump is being held in this way, and is melting, some dry sand, together with powdered slag from smithing which is completely free from copper or other contamination, is cast on the fire. For this purpose the best slag is that which falls from the iron when it is taken up from the bloomery and when it is cloven; this should therefore be collected and kept.
When the lump of iron and the slag have melted and fallen down in the forge the iron takes the form of a flat lump; the flatter it is, the better the iron. This lump is taken up immediately with tongs; on a large stone, which must be ready by the forge, it is held at the edge and cut into pieces as desired. Then it is ready to be worked up as one wishes.
In the first re-smelting process [of the day], the iron often loses some of its weight, most often when one is not well supplied with an ample amount of good quality slag from smithing, but if this is not lacking, and the smelting is continued, then only very little, or even nothing, is lost. It is therefore advantageous to perform many subsequent re-smeltings, directly following one another. That the slag and other impurities must of be cleared from the forge between re-smeltings goes without saying.
This re-smelting, and refining of the iron into the quality one wishes, can without doubt be done with less effort and more profit when one has the opportunity to build a little smelting-workshop including a trip hammer, in which both the bellows and the hammer can be driven by water. I have made a start at this but have not yet finished it, and thus cannot give a reliable description; especially considering that I have learned nothing of mathematics or mechanics, but must by my own reflection and experimentation find the correct proportions in the arrangement; whence it follows that attempts at various arrangements for this smelting and trip hammer workshop will perhaps in the beginning be unsuccessful.
When in time I have perfected it I shall with the same willingness acquaint my compatriots therewith, as I have acquainted them with bog iron and its transformation into iron and steel.
Chapter Nine. [Evenstad 1790:440-441]
About the re-smelting of fine iron to make steel.
When the forge has been used to re-smelt iron for almost a whole day, so that it is thoroughly heated through, it should be cleaned, dug up and pounded the same way as for iron-smelting, but the furnace must be 2 inches deep below the pipe (the tuyère) so that the air do not touch the steel once the smelting process has caused it to fall into the forge, then it is filled high over the edge with pine coal. One must then have ready at hand a piece of iron, as much as is remelted at one time, which after remelting must have been cloven in two pieces and then heated and welded back together, and on the anvil hammered out to a square iron bar. This is laid on the burning charcoal and when it has been well heated at the one end it is taken with tongs and held in the fire close over the airblast from the tuyère, but just high enough that the blast does not touch it. The fire must be strong and sustained, and therefore it is necessary that the airblast is constantly strong. With this the iron melts, falls gradually down in the forge, and becomes steel. Sand is cast on the fire 2 or 3 times during the melting, and after it [the iron] is all melted the strong fire is maintained and sand is cast upon it until the steel has settled, so that it can be taken up with the tongs, which is done very carefully, so that it does not go to pieces. As soon as it is taken from the forge it must be welded and hammered slightly and gently until it is evened out, then it is cloven with an axe into small strips and forged out and welded where it is porous, after which it is ready to be worked up. One obtains about half as much steel as the iron that was smelted for the purpose.
The bloomery bellows are more suitable in this re-smelting than the ordinary bellows of a smith; for by the use of the former the smelting is quicker and larger quantities can be treated at a time than with the latter.
Chapter Twelve. [Evenstad 1790:446-447]
Calculating the cost of re-smelting a Skippund [c. 160 kg] bloomery iron into fine iron, and the dividends thereof.
Two men working for two days can re-smelt 1 Skippund iron, and their payment is calculated:
The Master daily 32ß. - 64ß.
and the Assistant daily 20ß. - 40ß
The smelting consumes approximately
9 barrels of charcoal at 6ß. - 54ß.
The cost of 1 Skippund bloomery iron,
calculated in previous chapter - 2rd.32ß.
-----------------
Total 3rd.94ß.
[ß. = skilling]
[rd. = riksdaler = 96 skilling]
When, as I have mentioned in chapter eight, one has an ample supply of good quality slag from smithing to use during the re-smelting, has bloomery iron of good quality and performs the re-smelting correctly, then you should not loose more than 18 pounds from a Skippund [= c. 160 kg = 320 pounds]. To be on the safe side I will calculate the loss to 36 pounds, thus giving 284 pounds re-smelted iron, at the value of 3 riksdaler and 94 skilling. A Skippund re-melted iron will then cost 4 riksdaler and 47 skilling. This iron is of as high a quality or better than what the ironworks delivers at 10, 11 or 12 riksdaler for a Skippund. When the farmer needs to buy iron that expensive from the ironworks, and then has to transport it 200 to 300 kilometers to get it home, how profitable would not the bloomery production be for him instead, when he could make even more than he needs, and sell the surplus to others.
For those with the opportunity to build a smelting workshop, with water powered bellows and trip hammers, the re-smelting will become more cost efficent and less laboriously, thus increasing the profits from the iron.
Literature
Evenstad, Ole (1790): Afhandling om Jern-Malm, som findes i Myrer og Moradser i Norge, og Omgangsmaaden med at forvandle den til Jern og Staal. Det Kgl. Danske Landhusholdningsselskab, København.
Wagner, Donald B. (1990): Ancient carburization of iron to steel: a comment. Archeomaterials, vol. 4.1 (1990), page 111-117.