In period, it was typical to find two types of molds made for casting. One was a solid mold, made of stone, wood, dried clay, or whatever they could use for making the impression. Many of these types of molds have been found in various grave sites around Russia, sometimes multiples of the exact same designed piece with minor changes. These changes were most likely due to wanting the design a little different or perhaps even that before the change there was a significant flaw that continued happening and the change fixed it. The second type of mold was is a little harder to discern since it isn't something that could be found. This style of casting is known as sand casting where the piece they with to make would be pressed into sand or clay to take on the details and shape of the piece and then the metal would be poured within. Sand castings were always destroyed as you couldn't lift out the cooled metal with keeping the design in the sand, but you would be able to make many copies of something with less resources needed. All you needed was your one base piece that you would push into the sand again and again.
After a long time trying to decide how I would do this, I decided I wanted to try the plaster process:
- Make an ovular wax mold in the size and shape wanted for the brooch
- Push the wax mold into wet plaster to get the shape indented in it
- Carve the design into the plaster mold (instead of the wax where things would need to be the way they should as opposed to being carved into in mirror image, if that makes sense)
- Melt wax and put wax in the plaster mold to now get the proper shape needed
- Make a good half dozen molds in plaster by pushing the wax into the plaster
- To make the backing, lay a few pieces of waxed linen on the inside of the mold and then place talc or similar substance on the outer section of the mold before pouring new plaster down to form the backing.
As I was making these brooches to go with my Viking age Russian dress, I decided to make the brooches as similar to those that were found in the grave with the dress as I was able. I started with the easiest part, which was making sure they would be the proper size. The brooches that were in the find were 12.5cm long, so the wax oval was carved into that length. I then shaped it as the brooches were shaped, into an oval with a rounded top. I did not carve out the inside to make it into the full shape needed as I feared it would then be too flimsy and I needed to make sure I could push this piece in and pull it back out again.
Once the wax was carved into a very simple oval shape, I mixed up the plaster (a combination of potter's plaster and plaster of paris) and made an imprint of the oval within. I then began carving my design which was based on a period Russian brooch design from about the same century as they believe the dress was from. Unfortunately, the brooches that were found in the birch bark box with the dress only had shared photos of them from behind and not the design that was on the front. The brooches were so varied, though, with different designs in many different territories with people also most likely stealing them when they raided villages and wearing those as well, that I didn't feel the design to play a terribly huge role. I found the size and shape of them, since they were so big and a surprising find at that size, to be more important.
Once the design was drawn into the plaster, I allowed it to dry overnight. I should have baked it and probably would have had much less issues had I done so, but I did not for whatever reason. I melted down another chunk of wax and placed cooking oil into the plaster mold before pouring the wax inside to act as a buffer so I could get the wax out easier. Unfortunately, I hadn't noticed I had made some undercuts which became an issue as I tried to un-stick the wax replica, but I eventually had gotten it out. At this point, I added some extra carving into the wax to create more definition in the lines I had drawn before even starting to make more plaster casts to be able to cast into.
Once I had four plaster casts that I made with the wax replica, I decided it was time for the next important step. That step was to create a backing for the piece since I didn't just want a huge solid piece of metal. In medieval times, backings were made with waxed linen in the thickness you wanted your pin to be in the end being laid into the mold itself and then pouring plaster over top to make everything sit perfectly together. This can be shown in the fact that some brooches that have been found have, on their back, a linen pattern and sometimes even threads of linen stuck in the metal. So I waxed up my linen and made another large mistake. Although I laid my linen in the mold, before I poured the plaster, I decided to put waxed linen around the sides of the mold too so that it would be easier to get the two molds apart. This did two very importantly bad things: one, it created an uneven surface for the backing that caused me a long and painful time filing it to get it flat. And two, it made it so that the two layers of waxed linen that I wanted the thickness of my brooches to be ending up being incorrectly measured. The second time I poured the plaster so I could have another cast, I tried to fix this issue, but unfortunately, unknown to me since I didn't know much about casting, I had managed to let the fabric in the mold stick out from the edging too far which caused dire undercuts in the backing mold (which I didn't find out until casting).
I decided I wanted to test how well of a job I did and placed the most uneven packing on my original mold that had the more simplistic design, and poured wax in it and let it set. It seemed to work out well, but I didn't understand that wax had much different properties than melted metal, such as the fact it takes a lot longer to cool so I could pour the wax in the front of the mold and then place the back on top and it would still come out fine. I didn't understand that I needed a sprue and a clamp and everything for the metal.
I thought I was ready to cast, but I was very wrong. At first, I was going to cast in bronze. We set up a whole furnace, much like a furnace would have been set up in period, and began melting the bronze in a crucible while I was drying my molds in the oven. When I brought them out, I was informed that my molds would explode if I tried to pour molten bronze into them, which was the best of the worst case scenarios. I had used an incorrect material to make my molds and, although I had baked them to get all the water out, bronze heats to a much higher temperature than, say, pewter. Because of that it actually changes the chemistry of the plaster and forces some bonds to break which creates water molecules which then produces steam which, while trapped in a small area, causes explosions that could send molten bronze into the air. I decided I did not want that to happen and scratched that idea.
Luckily there was some lead-free pewter to play with, so we decided to cast in that. And, as I mentioned before, I didn't understand the properties of melted metal and so I did not have a sprue in my piece. We filed one in and packed sand around the mold to hold it upright because, as I didn't know, I couldn't just pour the metal in and then quickly place the backing onto the mold. So we propped it into sand and, because I didn't have a clamp, we mounded the sand up and around the mold. Once the pewter was melted we poured it into the mold and I learned I had made three large mistakes.
Mistake one: I had put a backing onto a front that was not made for that front. That meant that these two pieces were not poured to meet each other and so there was a large flash and we lost most of the pewter out the sides.
Mistake two: Again, because it was the incorrect back for the front, the thickness was completely off and it was much thicker than I planned on this piece being.
Mistake three: This particular backing was the one I had mentioned earlier that had severe undercuts. This meant that all the metal that we had melted and poured was unrecoverable unless we broke the mold apart.
Obviously the molds were not working for me, but thankfully I had my wax replica and decided this was a perfect opportunity to try out the second form of medieval casting: sand casting. The idea of casting concerned me because I heard many people tell of it going horribly awry. The process was almost exactly what they would have done in period only we used a special type of sand which has rough edges and then is rolled in oil and then in clay so it sticks to itself easily. We used an actual framework so that we could pick up the two pieces, back and front, and remove the wax replica to use again.
It went a lot smoother than working with the plaster did and gave me a fantastic cast that merely needed some trimming to make it work correctly. After trimming and studying the closures that were used in most pictures of medieval brooches, I knew what kind of spring pin mechanism to use.
The process was a tad bit more modern than I could have made it, but part of me also felt like I was doing things the medieval way. There wasn't so much differentiation that made it stand out as obviously modern. And now I have a nice pair of brooches out of it.
Many thanks to Lady Irene and Yvan Wolvesbane for all their help in this process.
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McCreight, Tim. The Complete Metalsmith. Sterling Publishing. 1991.
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