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Plaster Bass Relief Mold with Carved Lettering


Dick Bonham

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Hi,

I thought people might be interested how fine detail and lettering is created for Bass relief sculptures, medals and coins.

The piece I am demonstrating is a 1950's school crest for a one and one half life-sized bronze portrait bust but the techniques are identical for a piece of any size. This technique works especially well for anyone who wants to make a very small detailed wax for casting.

In the first picture The knight and horse have been sculpted roughly in relief and the boarders have been laid down in half round strips which have been extruded using a clay extruder. A wall has been built around the piece to contain the plaster. The next step is to brush on a light coat of soap diluted in water. Mix up a batch of Plaster of Paris and brush on a light coat filling in all the detail and eliminating air bubbles. Pour the plaster into the mold and allow the plaster to set. This usually takes about a half hour.

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The next picture is of the plaster after it has set showing the reverse of the knight and border. All of your letters are laid out BACKWARDS (making sure to use guide lines to keep the letters a uniform height). The lettering needs to be in reverse so the final positive will be correct. Don't be afraid to cut into the plaster a little bit with your pencil because any marks will be removed later in the process. I use square tipped tools (many of them dental tools) to carve the letters into the plaster. Make sure you don't have ANY undercuts in your carving. I will also refine the knight and his horse carving into the plaster any details I want to be raised in the positive. You can carve very delicate lines and details (for example vines, leaves, flowers and bugs) into the plaster. These details are almost impossible to sculpt in clay or wax working on the positive image. You can check your work by pressing small pieces of clay into your carving and looking at the positive image. Do not allow the plaster to dry during the carving because dry plaster is much harder to carve and it is also brittle.

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When you have completed all of your carving there are several ways to go from this point. If you are doing a small piece and you are happy with the clay positive you pulled from the plaster you can cast or press wax directly into your plaster mold. If you pour or brush hot wax into the plaster mold be sure the plaster is WET. Soak the plaster in water until the bubbles stop coming to the surface. Dry the plaster with a towel so there is no water on the plaster. You can then cast wax positives from the plaster mold. When the wax cools to room temperature the wax will have shrink so the positive piece can be removed easily. If you allow the plaster to dry and pour hot wax into your mold the plaster will absorb the wax and ruin your mold. If this is a detail for a larger piece you can use the pressed clay positive. If you want to refine the design in plaster you can pour a plaster positive and continue carving. To do that build a wall around your piece. Brush on the soap mixture. Mix your plaster, carefully brush on the first coat of plaster to fill in detail and eliminate air bubbles and fill the mold. When the plaster has set, CAREFULLY separate the two pieces by inserting a very thin blade at various places around the rim. If you have no undercuts you will have a perfect positive. If small pieces break simply mix tiny batches of plaster to repair those areas. Make sure your plaster is very wet when you do any repairs since dry plaster will suck water from the newly mixed plaster and it will never set properly. When your piece is finished make a rubber mold for waxes, plasters or cold cast bronzes.

Dick

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Here is the piece which was first sculpted in plaster, cast in wax now rendered in bronze. I thought this picture was interesting in that the artisan who chased out the final sculpture at the foundry used a hammer, chisels, files, scrapers and punches for all the fine work.

Dick

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Short and sweet- Thanks Dick. Though I may not find direct application for those techniques in my work, I'm filing that one away under "so that's how it's done". Would you ever lay text out on the computer first and then print it on Mylar, to create a stencil for lettering?

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Hi Dick,

 

thanks for the tutorial. Is always nice to see methods used by other artists. I like the way you modelling the knight. I myself used to carve the pictorial part of a medaille together with the lettering into the adverse and sculpt it after it is recast into a plaster postive.

Thanks again for sharing. :lol:

regards,

Karl

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