To make a mold, you do the sculpture and then build up your molding material over the sculpture, in two halves, front and back. To be fair, what some people call easy, others call difficult. Here is a basic description of how to make a mask mold, using ultracal and burlap, the simplest way to make a mask mold.
Two Piece Stone Mold for Slip Latex Masks
This is probably one of the easier two part molds. Typically Masks are sculpted in water based clay, but nowadays it seems more and mold people are using oil wax based clays. Regardless of clay type, this method works just fine. I like to seal the mask sculpture with 2-3 coats of aerosol acrylic lacquer and a coat of dulling spray. You have a choice with this type of mold. I like to do these lying down, but you can do it standing up as well. If the sculpture can handle being laid down to mold, I would highly suggest doing so. Be sure to protect the back of the sculpture with plastic wrap and some soft foam. Whether standing up or laying down, you will need to build you clay wall along the sculpture, dividing it perfectly in half front to back. You can use knobs of water clay to support the wall from behind if standing up. If lying down, just build the wall up from the work table. Typically these molds are strapped shut, so you do not need a flange. However, if you favor the clamping method for closing your molds, then make the clay wall about 2 ½ wide and add a lip at the end to act as a guide for the flange thickness. If you process without a flange, the make you wall about 1 ¼ inch wide. Be sure to add keys. You can also place a 1 inch wide collar of clay below the end of the sculpture to create a nice clean opening for the mold.
Once all of you clay is in place, add some keys along the wall. Either hex keys or half round keys would be just fine. Seal the water clay with a few coats of aerosol acrylic lacquer and a coat of dulling spray. Now you are ready to mold.
These kinds of molds are best made in stone because the latex needs something porous to cure in correctly. The harder the stone, the slower the cure time, but because you want this mold to last a long time, using Ultracal or Dental stone would be fine. If you need your pieces cured fast, use a medium weight stone, like Hydrocal.
Brush on your detail coat, building up a thickness of about ¼ inch. When it is dry by not hot, with a matte surface, you can mix the batch for your reinforcement coat, Rewet the surface of the first coat with some stone from this new batch and a wet brush. Now, start applying your stone soaked burlap. As always, I like to do this two layers at a time. Be sure not to trap any air bubbles between the detail layer and the burlap. Also, fold the burlap at the edges of the mold to create a nice strong edge. I would suggest at least 4 layers of reinforcement for this. When your reinforcement is finished, add a thick pasty batch of stone and smooth it over to make a surface coat. You want this coat to be no thicker than about 1/8 inch. Make sure during the whole molding process to avoid extended the mold material over the edge of the clay wall. This will just cause unnecessary mess and thickness.
When the mold is finished, cover with a plastic bag and allow to fully cure. When the mold is cool, remove the back and turn it over. Remove any protective plastic and foam, and then remove the clay wall. Wash off any residue gently and carefully with a soft damp brush. Now, apply mold release to the stone of the mold wall. You can use Vaseline or even paste wax, but I really like the aerosol petrolatum release because it goes on so thin. Also, be sure to add a few thin strips of clay to the wall in about 4 places or so to make pry points. I also like to apply release to the exterior of the first half of the mold to make clean up easier later. You can also add that collar of clay at the bottom of the sculpt to give the finished mold a nice clean edge. Spray everything with some dulling spray and then you are ready to mold.
Same as with the first half, start with a detail coat, building to a thickness of about ¼ inch. Then follow with at least 4 layers of stone soaked burlap, and a surface coat of about 1/8 inch. Be sure to avoid run off flowing down the first half of the mold and avoid a buildup of overflow at the edges of the mold wall. When the mold is finished, cover with a plastic bag and allow it to fully cure.
Now, you can remove the bag. If there was overflow and you cannot easily see the seam line of the mold then you can carve off the overflow using rasps, plaster shavers, and chisels. Try to do so a little at a time to avoid any damage to the mold. When the seam line is fully visible, then you can insert strong heavy flat head screw drivers into the pry points and slowly and carefully open your mold. Now, clean out all of the clay. For water clay, a few wooden tools and some water and a brush should be enough. For oil clay, you will need to use solvents with your tools and brushes to dissolve the residual clay. When the mold is clean and dry, you can patch any holes using a thick batch of stone and a wet finger or tool.
If your sculpture is more complicated you can do a 3 piece mold to ensure that it will open correctly without damaging the mold. Sometimes predators need a three or four piece mold. It depends on the sculpture. You MUST use WED clay or similar or Chavant NSP or similar for this, do not use air dry clay or the mold will not work.
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