Steve, that's a very interesting contribution to the discussion. But I doubt if there is actually more than a trace amount of silica in finished 1018 steel. The amounts in wrought iron would typically also be small, as most of the silicon content of the ores is greatly reduced by the addition of limestone or lime to produce slag. Here's some information I found on silica content in iron:
".... Silica (SiO
2) is almost always present in iron ore. Most of it is slagged off during the smelting process. At temperatures above 1300 °C some will be reduced and form an alloy with the iron. The hotter the furnace, the more silicon will be present in the iron. It is not uncommon to find up to 1.5% Si in European cast iron from the 16th to 18th centuries.
The major effect of silicon is to promote the formation of grey iron. Grey iron is less brittle and easier to finish than white iron. It is preferred for casting purposes for this reason. Turner (1900, pp. 192–197) reported that silicon also reduces shrinkage and the formation of blowholes, lowering the number of bad castings...."
It's interesting to note that silicon promotes the formation of grey iron which is "less brittle and easier to finish than white iron". So the presence of some amount of silica in the wrought iron used in Damascus could be either a curse or a blessing depending upon the percentage of silica content. We probably won't know what's in the amalgam of iron and steel used to produce old Damascus without an actual analysis done by a metallurgical lab. I worked in an integrated steel mill for several years after college and recall sending samples to the met lab during a heat and getting accurate results in short order, down to small fractions of a percent. Then the melter could add ingredients, or alter carbon content by blowing oxygen. They used Infrared spectroscopy then, and I wouldn't be surprised if mills use NMR now. The final analysis followed the product to end finishing and directly to the customer. Looking back, I wish I'd paid more attention and asked more questions, but often, the great object was simply not getting burned alive.
