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Plaster Master guide to home business                                    Work at Home pg 8

   Starting your own statuary business    

Making Production Molds    

Now that you have a new set of models, take this opportunity to clean up any minor imperfections that may have resulted from the mold making process or details you might have missed in the original sculpting.

Line 'em up and shellac 'em

After reworking your models with fine tools and sand paper mount them on boards and give them and the boards two coats of shellac.

 Brush, Brush - But Do Not Rush!

Make rubber molds on the
plaster models just as you did with the original plastiline model. This is a labor intensive project so don't rush it.  Let each coat  dry thoroughly in between applications. After you finish putting on a coat of rubber place the mold in front of a fan to hasten the drying time. There should not be any white showing on the mold before you put on the next coat.  A model this size ( 6")  will need about 12 coats of Cementex Latex rubber more or less, depending on how much you apply with each coat. Your mold will be between 1/16" and 1/8" thick when done. If you are using a brand of latex rubber other than Cemtex  you may require more coats to achieve this thickness. This may cause excessive shrinkage because it does not have a high solids count.

  All latex rubber shrinks. (Cementex about 2% to 3%) In fact you may notice that it has pulled away from the model in certain places as it shrinks.  Latex is a great material for concrete and plaster casting, things that are ornamental in nature. It captures great detail.  It is not a material for close tolerance work. This is a factor to consider early on in the decision making stage of your project. You may  need  to make your model slightly larger to compensate for the shrinkage. Urethane and silicone are better mold materials for close tolerance work.

Now that all the coats of rubber have been put on

let the molds sit for a few days to let the rubber thoroughly dry. One problem area is around the bottom of the statue where it meets the board. If you put on too much rubber in this area without letting it dry you will have a mushy distorted pour hole.(and that's something everyone wants to avoid. Right? )

Vulcanize!  Spock says so
Cure the rubber with heat, if you do not your molds will be weak and you won't get as many castings out of them.  Place the molds in a heating box or room that you have built your self or find a small tin shed,an abandoned automobile or any enclosure that gets up to 150° for 4 hours. Your kitchen oven may not have a low enough setting and there is danger of setting the mold on fire and burning the kitchen down. ( please don't ask!   I'm still getting yelled at for that one.)

Making the production mold backup shells

Take the mold shell from the original mold and give it a good coat of shellac if it's looking  a might peeked.

Then give it a couple of coats of mold soap. You know the routine. You're getting to be an old hand at this by now.

Place one of the new  rubber molds with the model still in it into  the mold shell half you just prepared.  You are going to use the old mold shell half as a pattern or form to simplify making the backup shells for the rest of the molds.

Fill in the gap between the mold and the back up shell with plastiline.  Press the plastiline down into the gap.  Make sure it is well sealed.

Then clean up any excess plastiline that may have gotten up on the rubber mold. That could affect the faithfulness of the rubber in reproducing an exact model. The plastiline can be spread out  on the plaster shell. That won"t affect the fit of the mold since the new shell will conform to the shape you are creating with the plastiline. The important thing is that you have a tight fit against the rubber mold. . 

Sometimes I put a few  extra coats of rubber on the first mold so that the cavity in the backup shell will be just a little bit larger. That allows  successive molds  that have less coats of rubber to fit   without having to trim material out of the shell.

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