portrait-sculpture.com

[Tamara]

Hi Everyone,

Here's a link to a mold tutorial on my blog.

http://tamarabonet.com/blog/2009/07/24/sculpture-mold-tutorial-of-wealth-sculpture/

Over the years, viewing the creation of numerous molds on sculpting forums, I was able to create a successful mold and took a photo diary of the process. The tutorial is really long but for those that are learning to do a mold, the added details are what really help.



~Tamara
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Happy Sculpting!

[Heidi Maiers]

Tamara, meant to comment on this tutorial sooner and forgot - sorry! Lots of good information there. It's fun documenting your processes, isn't it? You can't help but learn a few things yourself while doing it.

Interesting about the thinness you apply your bubble layer. I don't go nearly that thin. In fact, I would attribute those bubbles you had in the beginning to the moisture seeping out of the clay (you were able to get a better coating after the 3rd try because the surface wasn't quite as wet by that time.) You won't see those types of tiny blistering clusters of bubbles at any time when you mold plasteline. You do have to use an air hose, however, just to get rid of all the (slightly larger) random bubbles and air pockets.
After the rubber is on, a few more bubbles may make their way to the surface and you can carefully pop them with a toothpick while the rubber is still wet. I tend to put the first layer of rubber on ceramic clay a little thicker even because the weight of it tends to keep the tiny water vapors from being able to push it out and make those large sections of blisters. Like trying to blow air in a thick skinned balloon takes a lot more air pressure than blowing in a thin one to get it to expand.

Anyway, great presentation. Good you are a perfectionist - that means your molds will be perfect and save yourself a lot of work touching up castings later. Also, your molds will last longer and perform better. Great job!
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Heidi Maiers
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[Tamara]

What's confusing about the water vapor theory is that I sprayed a few thorough coats (being careful to not go to thick and lose detail) of shellac which should lock in the water. Then I put on my second coat in the same manner as the first, thick. I had oogles of bubbles.

Also, you know how I take quite a while with my sculptures, so this Indian woman was very leather hard, not full of a lot of water. So with the shellac I'd think it would really seal the remaining water inside.

Another point was that when I spoke with the gal who molded both my western woman and wine barrel lady, she said that she doesn't seal those with shellac. So I would think that even though she de-air's the rubber, the water vapor would have the same effect of making bubbles if that were the case.

It's all sort of confusing but one thing that's in favor of the moisture idea is that I did a test of the silicone on a fired and finished sculpture and had no bubbles at all. The coat of silicone was put on thickly.

So I have conflicting clues but the only thing that worked was to put it on very thin. Well, I'm just glad it turned out okay. Now I feel confident to mold most of my sculptures, I think. I'll probably do a quick and easy mold of the Luisa sculpture. She's all dried out now because I didn't keep after it with the spray bottle. Oh well, it'll be an experiment to see how the rubber works with dry clay.

Thanks for your ideas on the water vapor. That maybe what caused the bubbles, who knows!

~Tamara
_________________
Happy Sculpting!

[Heidi Maiers]

I agree Tamara, it's hard to keep a water piece from sweating unless it is completely dry. Especially if it is warm - above 70 degrees. Here and in California is hot this time of year, so best done indoors in the coolest part of the house. Also, I think the foundry may be using an excellerant or a different type of silicone that sets up faster? The faster it cures, the less time there will be for the condensation to occur underneath that first critical layer. Anyway, I think it's worth the extra effort on the mold making to be able to mold a wet ceramic clay piece. Yours turned out wonderfully.
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[Chris]

Hi Tamara,

Impressive piece and mould. Air bubbles are a problem in most silicones unless you use a vacuum chamber. I use a hot air gun. Just wave it over the wet rubber after you've painted it on and the bubbles rise to the surface and pop. Wet clay has never caused me any problems with air bubbles, I just think they come from the mixing process and the tiny ones join up with each other and get bigger.

Hope this is of help

Chris

[Heidi Maiers]

Interesting that you use a heat gun Chris. I would think that would make the water clay sweat even more heating it up like that. I always use an air compressor and blow the first couple of layers to get out all the bubbles, but the tiny fizzy ones we are talking about appear an hour or two later, before the rubber has set up. I think it's the length of cure time that causes the issue.
What brand of silicone are you using Chris? I've been using the Mold Max by smooth on, without an excellerator - and each layer takes several hours to set up enough to add the next and cures over night before the finished mold can be removed.
I've heard that Polytek PlatSil and TinSil are good rubbers, though quite a bit more expensive than the one I've been using. Would like to give these a try on my next mold job. Anyone have any experience with these, and if so, what is the main difference between the two (platinum based or tin based) and which would you recommend?
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[Tamara]

Well, I don't know what the reason is for sure of the bubbles but at least I know that putting the rubber on very thin is the answer. Thanks for the tip on heat gun, although that's a good point that Heidi made that it could cause more moisture to evaporate from the clay. I'd heard of breathing on the bubbles in order for them to pop, something in the carbon dioxide breaks the bubbles. I don't think it's such a great idea but it's just something that I recall as an idea to do. I think a person would need to do a lot breathing to get all those bubbles out.

For this next mold that I'm working on, I'll be using the accelerator on the first layer. Doing this will mean that I need to use smaller batches as it'll set up more quickly. I need it nice a fluid to get into all the detail areas. Thanks for all your feedback and tips.
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Happy Sculpting!

[Chris]

Hi,

It's just a gentle waft with the gun. You don't hold the gun on long enough for any heat to build up.

I use a 'quick cure' rubber from a local supplier which I believe is based on the polytek products. It starts to set off in about twenty minutes and cures in a couple of hours. The viscosity of the rubber is such that it doesn't allow you to build up a very thick layer at all as it just drains down the piece, leaving a very thin coating. Subsequent layers I add a fluid to increase viscosity and if I am filling very deep undercuts I add cabosil as well.
In my experience I have found slow cure rubbers much better for poured moulds as the air has time to escape before the rubber sets off. Certainly the QC rubbers seem more prone to air bubbles but as you say Tamara, providing the first coat is really thin the surface detail should be OK.

Chris