Our exploration of how a smith of yore would approach the challenge of heat treating comes to an end with part 4. The information in MS 3227a has lead us through examples of how a medieval crafts person was able to achieve their results based on experience and their understanding of the world. This peek inside the Medieval mind is important not only in the study of craft but in approaching most aspects of the study of this era. The observable world was their reference and they used the objects they saw to imbue their materials with characteristics exhibited by those ingredients.
Annealing, what is that?
The complete softening of a hardened item is referred to as annealing and is where the item is heated to critical temperature and then allowed to cool slowly to room temperature. This allows the carbon to transform the position it was holding in the crystal lattice and reduce the tensions. In essence return to the center of the cubes illustrated in part 3.
The last two procedures listed in MS 3227a are treated the same way as the hardening activities, but they evolved to achieve an opposite effect the lengthening of the cooling period which completely relaxes the stresses of hardening.
Next, if you wish to make iron soft and tough, then take one part chamomile flowers and one part ‘crane bill’ with blue blossoms and one part ‘veitbomes’, lay that all together in hot water and place that in a pot and cover it so that the brew doesn’t escape and let it fully boil. In that extinguish glowing iron, that will become fully soft and tough.
-note: Here chamomile flowers, crane bill’ blue blossoms and similar plants are combined in a pot. The smith is then told to extinguish glowing iron in the pot. Here the boiling vegetable stew is not quick enough to reduce the temperature of the item to harden it and the result is a tougher more ductile quality in the metal. We suspect this mixture would need to be fairly viscus to achieve its desired result.
The final recipe we are looking at is to make iron very soft. Quoting the text-
Next, if you want to make iron soft, thus take horn and scrape it on a (piece) of leather and heap that with ammonium cloride (sal armoniaco) and piss on that and wrap it about the iron and let the leather thus scald/sizzle the iron, thus it will soften.
-note: Here a slurry of sal ammoniac (ammonium chloride), leather and urine is wrapped about a piece that has been heated. The slow cooling of this medium will allow the material to get as soft as possible.
In fact the technique described here will insulate the heat from escaping as quickly. It will be much slower cool down than just being dipped or painted on. The use of ammonium chloride would also most likely help leave a clean well-prepared surface on the item as well. The same chemical was, and still is, used as a flux in preparing metals to be tin coated, galvanized or soldered.
The similarity of the treatment in the text between processes that both harden and soften the material indicate that the smiths of the medieval period saw the ingredients of their recipes as imparting certain attributes to the iron. While the understanding of the importance of temperature and carbon content are hinted at in the techniques they had developed, the realization these were the factors that mattered most was not realized fully. What is clear is they had evolved an understanding of material manipulation in such a way as to get consistent results.
The small list left us in MS 3227a opens a window on the complexity and depth with which the medieval smith approached their art. It shows us that while the materials they worked were inconsistent they understood them well enough to work them and manipulate them to their will. It is particularly interesting that the materials that have been chosen by the medieval smiths have constituent elements that have continued to be used in the smelting, refining and crafting of iron and steel objects into the current time. The functionality of these materials is obvious. Their achievements were accomplished without an understanding of the material science, detailed temperature measurement and accurate time keeping that the metallurgical world relies on today. The ability of the medieval mind to use the natural world and centuries of practical experience to master this area of material science demonstrates the power of their methodology and tenacity of commitment.
Heat Treating Today
A quick note to answer some queries we have had about heat treat today. The modern smith is most likely using a full quench and temper methodology in most of their items. This is accomplished by quenching in oils or salt solutions in most cases and provide very close tolerances. Industry standard is a two point range of target Rc hardness. As an example our blades are tempered to the range of 50-52 Rc. This is harder than the majority of medieval swords achieved but is a benchmark that most modern customers are concerned about.
Our heat treatment is done in molten salt solutions for the initial heat and the quench. This results in what is called a marquench, this provides a very tough durable blade.
Modern salt quench operation.
Translation by Keith Alderson, 2008, unpublished. Additional translations consulted unpublished Matt Galas 2002.