Technical Article: “Alternative One- Sided Molds for Pewter Casting” by Deanna Ooley

November 4, 2013

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I approached Deanna Ooley about putting together this article because I thought many other people might benefit from this thorough explanation of her approach to a basic public workshop activity. I know that many of us are often involved in demonstrations and workshops for the general public and this article might add another useful technique to the usual repertoire. I encourage everyone to share their feedback and other similar workshop approaches and experiences with us all. –James Thurman, Technical Article Editor

“Alternative One- Sided Molds for Pewter Casting” by Deanna Ooley

Ooley_Pewter01Recently, I was asked to conduct a workshop for 8-10 year olds. In order to illustrate the process of casting, I felt pewter was a good choice for simple pendants. I thought about what other materials could be used that were kid friendly, inexpensive, easily obtained, and quickly formed. I found that Play-dough served all of these purposes. The project also consisted of a pot, hotplate, soldering board, talc powder, a brush, bamboo skewers, buttons, and lead-free pewter.

The lead free alloy used in this tutorial contains 92% tin, 7% antimony, and 1% copper. What makes pewter both seductive and problematic is its melting point. At 480-500°F it is low enough to easily cast, not even setting wood on fire. Though, that same quality makes it the bane of silver and goldsmiths; cross contamination of such a low melting alloy with precious metals can lead to pitting and other issues.

When conducting multiple pours, purchase a small steel pot from the thrift store. Pewter can be melted on a stovetop or a hot plate. When performing a small single pour, a butane torch and a stainless steel spoon or ladle can be used.

Ooley_Pewter02Taking the steel pot, create a spout in its rim by tapping it with a large standard screwdriver and mallet. Chose a thick bottomed pot, as thinner layered ones tend to warp resulting in less surface contact with the hotplate.

Ooley_Pewter03As the metal heats, take a ball of dough, compress it on a flat surface for leveling, then push a button into its center about ¼” down. If pressed too deeply, the resulting item will create a sink hole as it cools. Buttons are a good choice for impressions as they are normally created without undercuts thus reducing tear-out  in the mold. Pinching a retaining wall in the dough is helpful in the event of a slight over-pour.

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Next a fine dusting of talc powder is applied. A soft brush ensures good coverage and the removal of buildup in corners. DO NOT SKIP THE TALC POWDER STEP. For Play-dough to be pliable, it has moisture in it. When molten pewter comes into contact with moisture, it will boil and spit, significantly increasing the risk of injury. The talc has the double duty of absorbent and mold release. The wetter the mold, the rougher the surface on the cast item.

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A talc covered bamboo skewer or toothpick can be placed into the design roughly ¼-1/8” in from the edge. Any closer, and the metal will not form around it.

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As with all casting, it is important to think about safety. Please wear protective eyewear, place the mold on a fire safe surface, have good ventilation, and have a fire extinguisher nearby.

In the melting process, the pewter will change various colors before it reaches its melting point. Often it develops a skin on its surface before it becomes liquid enough to pour. Avoid boiling the metal. Once it takes on the silvery appearance of mercury, it is ready to pour. Being quick is critical at this stage, as the metal will immediately begin to solidify once it is removed from the heat source.  When quickly performing multiple pours, melt more than needed and watch the mold fill point. Not over-pouring takes practice.

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If the piece doesn’t work out, just clean the item after cooling and place back into the pot for remelting. If foreign solids form, fish them out with a chopstick and put fresh metal in.

After the pour, the bamboo is only scorched and can be wiggled free. No drill bit is needed. If it becomes wedged, soaking the pendant after cooling will normally help dislodge the skewer or pick.

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The one sided molds afforded the opportunity for the children to witness both the liquid and solid states of metal. What the end-product lacks in detail, it makes up in accessibility, minimal clean- up, and instant gratification.

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Not everyone’s aesthetic leans towards the weathered look, though. Sandcasting is a similar process to the playdough, but affords more detail.  The item to be pressed cannot be too delicate or soft as pressure is needed to make an indentation; plastic or metal items are good choices. Hard wax or cured sculpy can also be used. Avoid undercuts in the design.

Pack and hammer delft clay into a steel catfood or tuna can, densely compacting the sand.  Press the object in the center of the sand until it is at least ½ way in. Compress the sand around the edges of the original item and remove.

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Dust the impression and surrounding area with talc and smooth with a soft brush. Pour directly into the mold. After cooling, remove the item.

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Any discoloration can be sanded and polished off. In addition to more detail, sand casting has the advantage of mold reuse. Just scrap off and dispose of the charred sand. The rest can be stored for future use; be certain to label it as “pewter only.”

Another open back mold option is traditional cuttlefish bone casting. Press your item into the largest and softest portion of the bone.

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You may wish to sand the back portion to make the mold level, but if the item is small just prop up the edges with clay or pumice rocks. Pour a small amount of metal into the impression. Have good ventilation and be prepared for the terrible smell that results from this process.  After cooling, release the item and dispose of the bone as this is a one-use mold.

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If your item is flat you may wish to cast with hardboard. Draw your item directly onto the surface and cut out. In this example, the negative space of an anvil contains a positive space hammer. The hammer is then sanded down to half the thickness. If you don’t like sanding, you may cut the two items out of two board thicknesses, the main silhouette should be created in the thicker. Glue the positive shape down to another board with Elmer’s glue or wood glue. Make sure to remove any excess glue from the seams before letting it dry thoroughly.

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Position the board with the cutout on top of the other board and clamp. Unlike the photo, please use metal clamps when available. Burnt plastic can be toxic.  Pour metal into mold, let set, then take boards apart. The boards may be a bit scorched, but can be reused. If the positive was not glued completely, it may detach and become embedded in the cast pewter item. Just soak and dislodge.

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Pewter is an excellent choice for other materials such as silicone putty, intaglio wood carvings, and cured plaster. Its low melting point and ease of use will allow you to make your own mold experimentations.

 


SNAG would like to take this opportunity to recognize our Corporate Members for their support: Facèré Jewelry Art Gallery, Halstead, Jewelers Mutual Insurance Company, K.M. Paulson Goldsmith Ltd., and Tim Roark Imports.

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