Properly preparing a model is half the battle won for making a mold. The original model – be it a toy, candle, figurine or even food item – is carefully cleaned and wiped all over.
The preparation varies depending on the type of mold making material being used. Artists zealously use an appropriate release agent in the right amount (when using any mold making material other than silicone mold rubber) to allow for proper demolding later. This will ensure that the mold does not bond to the model and comes off easily after curing.
However, many novice mold makers may fail to pay attention to the porosity of the model. They may be unaware that the original piece has tiny pores that can soak up some of the mold making material, leading to problems during demolding. Similarly, if the mold is porous, the final cast may fail to cure properly or even stick to the mold and cause distortions later on.
In general, models and molds made of wood, plaster, gypsum, unglazed ceramic, certain clays, stone, cement and concrete are porous.
Therefore, before beginning the mold making process, you should determine whether the model needs to be sealed first. Plastic, wax, plasticine clay, glazed ceramics, metals, fiberglass and polyurethanes are not porous and do not require a sealer. But if the model is permeable, it must be sealed appropriately before applying the release agent or silicone mold rubber. The sealer creates an effective barrier between the model and the mold making material.
Artists often use wax, paint and lacquer as sealers for their models. Clear acrylic sprays and alcohol-based sealers are available in art stores and do not interfere with the surface details of the model. Even sodium silicate is used as a sealer for plaster and concrete.
Water-soluble sealers are completely removable, while semi-permanent ones come off the model to quite an extent. The permanent ones will obviously stay on. In any case, it is better not to expect the model to return to its exact original form.
When applying the sealer, ensure proper coverage on the entire model or mold by using a brush. At times, multiple coats may be required. Solvent-based sealers need to be aired properly before applying the mold making material. In case, a sealer makes the model coarse, sand it down before moving ahead.
Your choice of release agent will depend on both the sealer and mold making/casting materials. Some sealers double up as a release agent too.
Once you have mastered these finer intricacies of mold making and casting, you can gradually move to making more complicated casts and even life casts of the human body. When working with life casts, always display the finished piece on an appropriate base with a personalized brass name plate. The brass name plate replete with your name and title of the artwork will lend the much-desired professional and gallery-like finish to your work!