W.I.P casting tutorial

[steve m]

I was asked by Tamara some time back if I would do a tutorial. At the time I was working on the piece I've entitled Independence.I promised her I would get around to one, so here goes. I like to model with oil based clay (plastiline) I prefer sulphur free because it is easier on molds. I like to start with aluminum wire for an armature, and bulk the clay on to that.

this picture shows the left hand in clay and the armature of the right hand






so now I bulk out the right hand and start stressing the emotion with the veins and musculature



this picture shows when everything is toned down a bit and ready for casting.This piece was intended to show someone breaking through barriers so originally I decided it needed to show the head coming through as well, so to start the head I actually use chicken wire and an expandable foam



To develop a base I actually mold the chicken wire over the top of my head to retain the correct deminsions, and end up with this.



I then fasten this wire to a piece of board and begin filling the inside with the expandable foam.

This picture shows the piece after the foam has set and it has been carved back down.Clay is then modeled on top of this.





I then create an armature out of foam for the base and begin modeling the clay for that.



This image is of all the pieces together and ready for casting.


The next step in the process is on to the mold making. I usually use urethane rubber for my molds. The first step in the process is to hang one of the hands and coat the piece with a release agent. you can buy release agent in aerosol form or you can make your own. (I make my own release agent by melting 8 ounces of vaseline in a metal container and then mixing it with a quart of mineral spirits.) I like to spray my pieces with a fine mist before I start to mold them and give them a little time for the solvent to evaporate before I apply the rubber. It is also a good idea to make sure you put a piece of plastic or something under the area where you are going to be applying the rubber.



Now that the solvent has evaporated I start to apply the rubber. I put the first two coats of rubber on very thin to make sure I capture the details of the lines. This rubber is so thin it will actually run off the piece (hence the need for the plastic on the floor.) This leaves a very thin film of rubber and you must add to that with additional coats.



For the additional coats I introduce cabosil into the rubber. Cabosil is fumed silica, a very fine powder that acts as a thickener. This helps achieve the thickness needed to give the mold more strength. At this point I also cut pieces of straws and inserted them into the ends of the fingers where air would have a tendency to trap.



Next I made a quick mold out of plastiline and poured some shims and keys that would be added to the sides of the rubber mold to create a dividing line.

image of shim molds



shims after poured and set up


Now I attach the shims to the rubber with toothpicks to hold them in place and start liberally applying rubber, enriched with cabosil.

In this image the shim on the left is already in place and I am applying the shim on the right. You can see the the rubber with the cabosil really increased the thickeness.


I let the rubber setup and place some square pieces of rubber (from the earlier pour with the shims) to create keys for the mold to fit in the mother mold.

I attach these with a little bit of the same rubber.

[steve m]

Next I build a fence around the piece with clay and spray the entire thing with release agent, in preperation for a fiberglass mother mold.



After the the solvent has time to evaporate, I start laying the fiberglass for the mother mold. I brush a little resin on the piece and the place pieces of fiberglass mat on this and apply more resin. I usually apply two coats of mat to build up the mother mold to the desired thickness. after this has set up I turn the piece over remove the clay shim and coat the underside of the fiberglass shim liberally with vaseline. This will allow the next application of fiberglass not to adhere to the first one. I have tried to just spray this with regular release agent before but it is harder to seperate than with the vaseline coat.

in this image you can see the keys that were applied and the shim created by the first side of the mother mold.


I then apply the fiberglass to this side just as before.

Here you can see the finished fiberglass with the keys in place. You can also see that I have drilled the mother mold for screws that will be used to hold the mold together when casting. I do this before I seperate the halfs to insure proper placement when I put the two halfs back together. Now I seperate the pieces and cut the rubber where the dividing line was created and take the original out. Clean the mold and apply a release agent.



Now the mold is ready to cast. To cast this piece I chose to use Resin with a granite dust. This is basically what is used in the housing industry for granite countertops. To pour this You mix the components by weight . The recommended mixing ratio for this product is 30-35% resin to matrix by weight. This is fine for pouring the head or the base because they were a open top mold which the mix could be poured directly into the spaces. As for the hands the resin content had to be bumped up a little bit for ease of pouring. Where the straws were initially in the ends of the fingers left air holes. I poured the mix into the mold, when the mix started coming out of the ends of the fingers with consistency I pluged the holes with a little bit of clay. I then took a mussle massager ( one of those vibrating thingies) and hold it against the side of the mld for about 30 seconds. This helps to work any trapped air to the surface, helps to eliminate air pockets. I then let the mix setup until the mold is cool to the touch. Demold.



I then sand the piece smooth with steel wool and apply a patina. The patina I use is a resin dye. I paint it on and wipe it off with a damp cloth. This virtually coats the piece and then I use a scotch brite pad to burnish this back to the color and effect I like. Then the process is the same for the rest of the pieces.

[steve m]

[steve m]

In order to save space I didn't show the other molds, but if anyone is intrested I can show you the finished molds for these pieces too.

[Rob Hendriks]

When I saw the hands at first I though you maybe has molded them from your own hands,that realistic they are!
Great tutorial I will study more close again.

Rob

[Lady Rando]

Great tutorial. I do have a question. Do you remove the plastiline shims before you make the clay fence? Guess I'm not getting that part clearly in the brain.

[steve m]

Originally Posted by Lady Rando

Great tutorial. I do have a question. Do you remove the plastiline shims before you make the clay fence? Guess I'm not getting that part clearly in the brain.

Tamara are you meaning the rubber shims? that were attached in the say 14th pic.? assuming thats what you are talking about. Those become incorporated in the rubber mold. I should have mentioned I put release agent on one side of them and build up the rubber to that. When hardened that becomes a seperating line. All you have to do is pull that part back and there is only a thin layer of rubber to cut through to access the original. yet there is a significant layer to nest up together to keep the mold oriented. I hope that was the answere you were looking for.

[steve m]

Thanks Rob for the compliment.

[Heidi Maiers]

Nice demo steve - and very cool sculpture! I love seeing how other people make their molds, etc.

[sculpturedolls]

Thanks Steve for that tutorial. I picked up quite a few little tidbits that I'll file away for later use.

Thanks for all the time you put into that to share with the rest of us. It was well illustrated and written.

[Lady Rando]

Steve, I posted a link to this tutorial in our Links to sculpting tutorials sticky at the top of the forum

[yogi]

Thanks. This tutorial comes at a perfect time for me, since I've been doing a lot of research (without actually DOING yet) about molding and casting. Great techniques you've used. I like the tip on the homemade release agent (and thanks for giving the proportions to use). I like the use of screws to hold the mold halves together, too. Haven't seen that done by anyone else in my research thus far. Again, thank you for taking the time to show us how you do this. I may come at you and others here with all kinds of questions when I start doing this myself someday. So please don't disappear!