Wednesday, September 5, 2012

05 Molding Design Nº 6

Many of the book resources I have, recommend hot-pour moulage for making molds directly on human skin because the moulage is inert. I do not recommend hot-pour moulage for making molds over human skin. Instead, I recommend using Dental Alginate to make molds for Life Casting projects. Dental Alginate is a use-once mold material in a powder form that is mixed with Room Temperature water to make the mold material. Dental Alginate is also inert, and cannot harm human skin. It is much more expensive than hot-pour moulage, but the risk of burns is nil. Click on any image to enlarge it.


Moulage is an alginate-like material made from kelp. Moulage is different from other alginates in several ways.

1. It is a globby seaweed gelatine even in its bulk form. You will find it shredded and moist when it is taken from the package. This moistness is what makes it good to use as a mold material for casting carving wax.

2. Moulage is hot-melt. When you heat it to about 150 degrees Fahrenheit it becomes fluid and formable. This is a minor dis-advantage.

3. A big advantage of moulage is that it is completely reusable. Simply reheat it, adding moisture occasionally as it dries out, to make it fluid and reusable.

Unlike plaster, which is a rigid mold material, moulage is semi-flexible, and can be used to make molds of objects that have slight undercuts, which would not be possible in a plaster mold.

To use moulage, remove it from its airtight container and drop it into a pot. Do NOT use an aluminum pot. Stainless steel, porcelain enameled, or glass pots are good utensils to use with moulage. If the moulage is not moist and properly jelly-like you might have to add a small amount of water. Heat the moulage in a double boiler till it begins to melt and flow. The melting point is low (about 150 degrees F.) so it will become liquid in a very short time. 

Use a wide-blade spatula to mix the heated liquid moulage. The wide blade is useful in squashing the solids against the side of the pan, and in breaking up lumps. Soon, the combined effect of the heat and stirring will produce a creamy paste.

The model to be molded should be surrounded with a suitable retaining wall. Pour the liquid moulage over the model until the model is completely covered at least an inch all around. Cover the mold with a plastic bag and let it cool.

The moulage is semi-flexible, so it can be slightly flexed in order to remove the model from the mold. Water and wax do not mix, so a moist moulage mold is perfect for casting carving wax. Moulage molds can also be used to cast plaster. For best results, a moulage mold should be used almost immediately. Moulage has the same drying and shrinking characteristics that all alginates possess.

Because moulage is semi-flexible, it is a good idea to use some sort of mother mold to support it, otherwise some distortion may occur, due to the weight of the material being cast. One piece poured moulage molds may be cut open easily, using a mold knife.

The advantages of hot-pour moulage outweigh the dis-advantages. Because it is reusable, it is an economical mold material to use instead of water-saturated plaster rough shell molds for casting carving wax. With care, two or more carving wax castings may be pulled from a moulage mold.Moulage makes detailed molds which produce detailed carving wax castings. Once the castings have been pulled from the moulage molds, the molds are chopped up and put back in air-tight containers, to keep the moulage from drying out. To reuse moulage, simply heat it up in a double boiler until it melts and becomes creamy, then pour it over the model in a suitable mold box.

The dis-advantages of hot-pour moulage are that it must be heated to become liquid; and because it is semi-flexible, it must have some support to keep from distorting when the casting material is poured into the mold.

For molding oil-clay doll parts, hot-pour moulage molds are an economical substitute for plaster rough shell molds, for casting carving wax doll parts. Moulage does not stick to itself, so multi-piece moulage molds may be made in a similar way that multi-piece plaster molds are made. The oil-clay doll parts do not require a mold release because moulage doesn't stick to anything.

To melt moulage in my studio, I use a stainless steel stock pot which sits on a stainless steel steamer plate inside an enameled pot on an electric hot plate.

The stainless steel steamer plate inside the enameled pot.

The stainless steel stock pot fits inside the enameled pot, and sits on the stainless steel steamer plate.

This is melted, liquid moulage in the double boiler with a wide blade spatula for stirring and mashing lumps.

After use, moulage molds are chopped up and stored in air-tight containers until the next use.

Published information about hot-pour moulage is difficult to find, and is usually more about making molds for Life Castings than for making molds of non-living objects. This weblog has documented several experiments using hot-pour moulage to make molds for casting carving wax. Simply search the weblog using the label: moulage to find such entries.

Here is a 1937 magazine article about moulage.

Excerpts about moulage from The Materials And Methods of Sculpture.

A source for buying moulage and posmoulage materials is Dick Blick art supplies.

These moulage instructions are in a PDF file: moulage_instructions.pdf


The Prop Builder's Molding & Casting Handbook. Thurston James.
The Materials And Methods Of Sculpture. Jack C. Rich.

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