A friend asked me recently if I ever weave with silk, my initial answer was no. Then I remembered a number of years ago I had woven a set of silk garters (lefg) for a friend and a silk belt on my rigid heddle loom, but it was not fine silk. I have seen a number of lovely silk weavings posted on Weavolution, which inspired me to order some more silk and in a smaller size. Around the same time, I noticed my notes on cotton cloth in the Middle Ages and began looking into organic cotton. I ended up ordering 12/2 natural silk, 8/2 unmercerized cottong and 10/2 organic cotton (which is so soft and wonderful to handle by the way).When the orders arrived, I got very excited about weaving with all of these yarns. I started planning a silk twill block project, inspired by a Roman textile I ran across recently, and was going to use 3 colors, 2 in the warp and 1 weft. I ran out of the cone of silk at just under 2" of warp, so I had to use 4 colors in the warp. This change in plan made me wonder just exactly how much the prices compare for these yarns. Most weavers who do historical re-enactmet would site cost as the main reason they substitute cotton for silk. So I decided to put together a little comparison and put this to the test. I had ordered mini cones of the silk, so I could sample with a variety of colors and see how the colors interacting in a variety of structures. I had ordered 2 different amount of the 8/2 and 10/2 cottons. As there are 3 different weight to factor in, I calculated the cost per one yard of thread (total cost divided by estimated length on each cone). Here are those results:12/2 silk $.05 per yard8/2 unmercerized cotton $.005 per yard (yes the number of 0's behind the decimal point is correct)\10/2 organic cotton $.01 per yardObviously the unmercerized cotton is the cheapest per yard, but I'm not sure how it compares to the historical cotton. Even unmercerized cotton is hard spun and often ring spun, processes that were not available in the Middle Ages. At first glance I though well 1 cent versus 5 cents isn't that much of a difference, we're talking pennies right, but is that a fair comparison. So I'll just start buying silk from here on out, then I thought about that mini cone that didn't even have 2 inches of warp on it. So I ran some more cost comparisons.Yes comparing the cost of one yard is heading in the direction of comparing apples to apples, but does it go far enough? I decided it does not, because yarns of different weights use different setts in the final cloth and when you're talking about weaving 30" wide cloth this could be a big difference. So next I looked at the theoretical sett for each yarn and how many yards of yarn you would need to produce a 1" wide, 1 yard long piece of cloth. The cost for this scenario is:12/2 silk $ .698/2 unmercerized cotton $ .1010/2 organic cotton $ .34So you might be thinking, yeah the silk is twice as much as the cotton, but 69 cents isn't much right, why aren't more weavers using silk? Well you need 30" wide cloth for a less than average sized person and even if you are being really careful about the cut you need at least 6 yards of cloth for a woman's dress. I used a balanced plain weave sett for these calculations. So if you are weaving a decorative piece that is small your cost for the materials isn't going to be much, so go all out and use silk! However weaving silk cloth for a dress you are likely going to weave twill, damask or satin, which for clothing requires more than twice the sett of plain weave. So the cost of materials alone for a silk dress using geometric construction (i.e. a method of construction that has very little waste) would cost you $290, about $40 a yard. For all those who have $40 yard to spend on materials and the hundreds of hours to weave a silk garment, go for it! But for those of us with less time and money on our hands, use silk for smaller projects and know that you are correct if you say that you substituted cotton thread for silk due to cost conerns.I think this also reiterates what "kingly gift" silk fabrics were in the Middle Ages. If materials alone are $40/yard when we can ship via airplanes and mass produce thread, how much did this cloth cost without those advancements. If you have run across information on this topic, please do share it here!