Post #377955 by Babalu on Sun, May 4, 2008 12:21 PM

OceaOtica - Really good post! I'll have to remember to try the alcohol thing. I love the fact that other folks are jumping in and sharing their own knowledge. In fact, and I'm sure Bowana would agree, I'm going to change the thread name to "Plaster Mold Making & Ceramics Information" in hopes that other TC'ers will follow your lead. Also, I totally agree with you that it would be really helpful for beginning sculptures to start out playing with regular water based clay first...Hell, for that matter, there is no reason you can't make a mold off of a glaze fired ceramic work too. You might loose a little detail this way, but hey...

If you are just beginning to play with sculpture, you might also consider jumping into a beginning clay class at your local community college. These classes are always fun, and I think one tends to learn quite a bit in them...Plus they are cheap! One of the best teachers I ever had was in a community college setting...For me, I feel I learned just as much there about clay as I did in the grad school I transferred to later on.

Cammo, your right. Your mug shrunk only 6%. I hadn't put a ruler to it before...it just felt double that to me. I put the master sculpt of Oki next to a fired finished Oki here so you can all see what 6% looks like. A 6% reduction in size may be a concern to someone whom needs a mug to hold a specific amount of liquid. Like you said, it's really up to the person. Henrik and Kaimuki, I would bet your are seeing a higher shrinkage rate than this 6% as your final firings are much hotter? A really, really important point to consider when sculpting your master is "how does it feel in your hand"...how will it feel when it shrinks a little?

This picture below is also a good picture, because it shows how the master oil clay sculpt weathered the whole mold making process. Not bad, huh...one could quite easily do another mold from this master without having to do much to repair it. I have seen where other people are using their master sculpt to cast a harder master resin copy first. This way, one could build multiple plaster molds for mass production. There is a good thread showing this somewhere on TC...hopefully someone can post a link to it on this thread? I can't seem to find it.

Another thing, If you look back on the pictures, you will see that we built the finished master up around the top with our oil based clay. This extra space added is needed. When you pour your slip into the molds it shrinks down from the top as the clay is starting to settle and harden in the mold. The clay thins in this "extra space" area. After you have pulled the slip casting from the mold take a knife and trim this extra off the lip of the mug. Dip your finger(s) into some water and smooth out the rim. Be gentle...keep your rim rounded. Remember liquid needs to pour from your mug and look good doing it.

Kaimuki - Love your new mug! You might also want to test a lower fire slip too? What type of problems are you seeing with the cone 5 slip? "Babalu - do you make your own slip" - Nope, I didn't make my own slip for these mugs...I guess the reason is because, it's really easy to just go buy the pre-made slip quite cheaply, and this store brought "pre-made" seems to be always made well. Cammo found some gal here locally (San Diego) that is making slip for a reasonable price too. I think if I were really into to punching out a large number of mugs (100's), then I might make my own slip as well as making multiple molds to use for one design.

Mad Dog - No worries at all. I think it's cool that someone has starting giving this whole mold making thing a shot.

I did a quick online search for a simple tell all about loading a kiln, firing, trouble shooting glazing, etc...I grabbed these two without looking around too much...there is tons of info online these days about ceramics. We are only just touching the surface....

http://www.clay-king.com/conefire.htm
http://www.ceramicartspace.com/firing&glazes.php