There are many brands of RTV (Room Temperature Vulcanizing) Silicone mold making compounds on the market and available to sculptors today.
Shown in this tutorial is Amazing Mold Putty.
This two part compound is sold in 2/3 pound boxes and also in bulk; check their website for more information.
The set comes with complete (and well written!) instructions for use, and two containers, one of Part A and one of Part B as shown here.
Separate, the two remain waiting for use. However, when mixed, the two parts firm up within minutes.
Have your originals available and ready to cast before you start to combine the two parts.
Temperature also affects set-up time, and the mixed putty cures faster in warmer temperatures.The warmer the temperature, the shorter the work time and de-molding times will be.
|Equal parts of each by weight or by volume are mixed in a 1-1 ratio.
Roll and squash the yellow and white portions between your hands quickly and firmly to blend to an even color.
It is best to achieve this in a minute or less.
As a general rule of thumb, you want to mix an amount just a bit larger in bulk than you used in creating the original piece.
It is helpful to have a small item or two ready to cast at the same time just in case you mix up too much–it wont stay workable for more than three or four minutes.
During that three minute time frame, mix the putty together thoroughly and then roll it into a smooth ball.
Start with the high point on the item–in this case the nose–and begin to press the putty over the original.
Working quickly, press the silicone all around the original piece, making sure good contact with all areas is achieved.
Fabulous detail can be gotten with molds cast in this manner, but only if the putty is in contact with them!
Continue to press into place until the original is completely covered.
Be careful not to expose any portions like the tip of the nose!
Remember to work fast, and then stop–do not rearrange the compound after it has started to set up and harden.
Use enough putty mix that there are no holes and at least 1/4 inch around the sides.
The picture at left shows the back of the mold and original but DO NOT flip your mold until it has had a chance to harden up completely.
Moving it around during curing will deform your mold.
The putty will stick to itself, and if you have thin parts after de-molding, an additional amount can be mixed and used to reinforce the thin spot.
However, be sure to completely cover all areas on the first layer as patch lines will otherwise show on your pulls.
Although you can make VERY thin molds and texture sheets, faces take bit of pressure to fill and the mold will last for many years and hundreds of pulls if properly made in the first place.
Allow the piece to rest in the mold undisturbed as the silicone cures.This can take 20-25 minutes at normal room temperatures, or as long as 40 minutes if the room or the putty is cold.
It is better to be patient a bit longer and create a clean impression.
Curing time can be speeded up by heating under a heat lamp or in an oven set to 150 degrees F for 10-15 minutes.
When the mold is completely cured, you will be able to poke it with a tool or fingernail and not have any deformation of the surface.
The rubbery mold can easily be flexed to release the original.
The mold and original shown above display the detail that is possible.
If there are minor flaws in the mold because the material was not in full contact with the original, don’t despair, as these flaws can often be easily fixed in the smoothing and refining of each pull made from the mold.
I have better results if I allow a mold to rest several hours or overnight before its first use.
While waiting, I’ve mixed an ivory colored clay using white, translucent and ecru.
This mix gives me a faux-ivory that I find very appealing.
However, any color can be used, and it need not even be fleshy at all!
Red clay makes lovely devil faces, and masks come in all sorts of colors.
Whatever the color, start with a ball of clay and then shape one end into a bulbous point.
Make sure that the clay is fully conditioned and warm enough to be easily pliable.
Unlike polymer clay or plaster molds, these flexible molds require no mold release when using with polymer clay and most materials.
When using ceramic clay, Badger Balm or olive oil makes it much easier to get a clean pull.
Press the point of the ball of clay into the nose cavity.
If you do not start with that point, the resulting nose will be flat as the clay will not fill the cavity as would a liquid like melted soap or chocolate.
Press the clay into the mold firmly.
Fill the entire space and push evenly and thoroughly into the mold to get the best detail.
If you have too much clay the piece will overflow the mold, and this is not desirable when making face masks or faces meant to be glued to a flat surface.
If this occurs, simply remove the clay and start over with a bit less clay.
Once you find the “just right” amount, you may wish to cut many equal pieces if you are making several at a time.
You can also use smaller amounts and only fill part of the mold, and this results in some very interesting fragments.
|For ease in removing raw clay with little distortion, use a puller piece.
This is simply a warmed up chunk of clay that is pushed firmly onto the thick part of the piece.
Lift and pull the clay from the mold.
I usually make use of a scrap of the clay that is being used, as strong colors may leave a visible residue on the back.
Try to do this from the middle or top sections but not the edges as smaller thinner sections are more easily deformed.
If you do it from the chin area, the nose will be pulled upwards and may be difficult to reshape.
If you are having difficulty getting a clean pull from the mold, make sure that the clay is warm when it goes in, and then allow it to rest and cool before removing the clay.
As polymer clay is thermally reactive, it softens when warm and becomes more firm when cool.
If you are having a heat wave and the clay is particularly sticky, put it in the refrigerator for ten minutes before removing from the mold.
However, leaving clay in the freezer is not recommended as clay will “weep” plasticiser as it warms up and be more sticky and less strong after baking.
After removing the pull, smooth and refine the surface of the clay as needed.