Lost Wax Casting Brass Award Medallions
Created by
Sir Jonathas Reinisch, OP Barony of Dun Carraig Kingdom of Atlantia
MKA James Kriebel [email protected] The Concept
The project started simply enough, with wanting to replace the carved bone medallion I had received when granted my Kraken. Unfortunately, I had passed that medallion on years ago, and from there it had passed on again. I found a sibling of my medallion in the hands of another member of the Kraken. In trade for borrowing his medallion, I promised him a copy of his medallion in brass so that he would be able to pass on the original while still keeping a copy of it. Needing a method of casting where I could return the original work to its owner quickly, I could not use sand casting as the original needs to be pressed in sand every time. This project required I go with Lost Wax Casting, specifically Indirect Lost Wax Casting where I could make an Intermediate Mold then quickly return the original.
Being a Pelican, this started me down the road of unwittingly volunteering/challenging myself to create my own design of the medallions for the other various Atlantian Awards. This documentation will focus on those medallions created by my own hand with my own design for each award.
Original Artifact
For this process I had no original artifact per se, but rather started only with the drawn representation for each award from the Atlantian Order of Precedence.
Figure 1: The Original Images from the OP Method of Creation
In the past, I have used Sand Casting for the Fox on my Knight’s Belt, and Lost Wax Casting for the Bone Carved Kraken. When I decided to continue this project into making medallions for many of Atlantia’s awards I decided to go with Lost Wax Casting, as it had returned more consistent results when trying to make multiple copies.
(1) The original for each award was carved from hard jeweler’s wax using various clay and wood carving tools. Careful attention was given to details and smooth surfaces especially in those places where I was planning on adding enamel to the finished pieces.
Figure 2: The original carving
With ‘Indirect Casting’, wax copies of the original are made. For these copies, I used a (2) silicone molding compound which allowed me to quickly create the intermediary mold. Using this intermediary mold, I created secondary wax copies of the original carving in a soft low temperature wax. This secondary process allows multiple copies to be made from a single original at the cost of just a tiny bit of detail and sharpness.
Figure 3: The intermediary mold and secondary wax
With a secondary wax copy now available, the normal Direct Lost Wax Casting process picks up. To the secondary wax are added sprues, which allow the molten brass in, and (3) gates, which allow the air out. This wax tree is then cast into an investment mold . For these small pieces I used simple inexpensive plaster. The downside to using plaster is that it is likely to expand and crack at high temperature. This was countered by keeping the plaster mold in a metal sleeve.
Figure 5: Plaster molds waiting to be cast (4) The investment mold is then placed in a kiln to burn out the wax, leaving a void where the wax was, hence the name ‘Lost Wax’. Not having access to a true kiln, I used a standard kitchen oven for the lower temperature steps, slowly bringing the investment mold up to high temperature over several hours. My final step was to place the investment molds directly above a propane burner which brings them up to 700 degrees Fahrenheit for an hour before casting.
At the same time the investment mold was in the final heating stage the furnace was (5) used to melt the brass. Once the brass was fully liquid, a pinch of Borax was added to remove impurities. Then the investment mold was removed from the heat and the brass was poured in to it. As I do not have a kiln and my molds are not at the highest possible temperatures, in a straight gravity pour the brass cooled too much to reach into all the (6) fine details and corners. To overcome this I have begun using a spin caster which has the effect of dramatically increasing gravity, helping the brass to flow into the mold quickly before it cools.
Figure 6: A mold on the spin caster
Once the brass and mold have cooled, the investment mold was broken open revealing the cast medallion in the center. At this point the brass was black and gray with burnt investment still stuck to it and still have the sprues attached. The medallion was then cleaned up and finished by cutting off the sprues, using wire brushes to remove the burnt on investment, and files to remove any burs that were caused by imperfections in the mold. Finally the medallion was polished to the level desired.
Figure 7: A casting just after breakout from the mold
Figure 8: A casting after cleanup and polishing
At this point the casting process was complete, however the medallion still needs to be finished with any enamelling, plus a chain.
Figure 9: Completed medallions
Differences from Period Technique (1) Jeweler’s wax is a very hard wax which is hard enough to hold sharp edges and fine details, but ductile enough to carve smoothly. While being wax allows replacing chips and mistakes by remelting a bit of wax. Historically this would have been waxes (historically softer), clay, bone, or wood.
(2) Historically molds for making the secondary wax copies would have been made using a clay slurry, allowing it so slowly dry over the original carving in repeated layers to capture details before a thick outer clay layer was added to give support and structure. Once fired this would leave you with a smooth but very fragile surface to cast the secondary wax copies from. The silicon is poured over the original in much the same way, only is much less fragile allowing for more secondary wax copies to be easily made.
(3) Historically the investment would have been made by alternating clay slurry coated with fine sand, allowing each double layer to dry, building up multiple layers until thick enough to stand on its own. Water soluble investment, such as plaster, drys much quicker allowing me to cast and still have a full time job to pay for the hobby.
(4) Historically the furnace would have been coal fired with multiple manually operated bellows which could get hot enough to cast iron as well. For brass casting the furnace only needs to get to 1800 degrees Fahrenheit to melt the metal and to bring the molds to around 1600 degrees Fahrenheit to allow gravity fed casting to reach all the small details before cooling.
(5) Borax is obviously a modern addition to the process. I have not been able to find out if, or how, the impurities were removed in period.
(6) A spin caster greatly increases gravity by spinning the mold at high speed as the molten brass is poured in. The effect is that the brass flows much more quickly and is then pressed hard into all the fine details before it can cool enough to solidify. The downside is that the molten metal will also cast into even the smallest heat crack as well.
Self Criticism Time and Money. With more of both I could have attempted to replicate the medieval process much more closely. However with the constraints of a full time job and a family a few modern replacements had to find their way into the process. Likewise, not having access to equipment even remotely similar to the medieval counterpart forced some changes as well.
Credits Many thanks to Mistress Molly, Master Chris, and Countess Lynette for help and guidance with this documentation, and then my Lady, Baroness Amalia for her translating my poor attempt at Inglesh into legible English.
Even more thanks to my Lady, Baroness Amalia, for putting up with me stinking up her kitchen and oven in the early steps of “baking” the molds.
Sources M. Martinón-Torres and T. Rehren (2002): Agricola and Zwickau: theory and practice of Renaissance brass production in SE Germany; In: Historical Metallurgy 36(2) 2002 pp 95-111.
D. Dungworth and M. Nicholas (2004): Caldarium? An antimony bronze used for medieval and post-medieval cast domestic vessels; In: Historical Metallurgy 38(1) 2004 pp 24-34.
N. Miiks, C.Tulp, and A. Soderberg (1999): Precision lost wax casting; In: Experimental and Educational aspects of Bronze Metallurgy pp 56 - 78