Mold-making is something I don't normally do to make my ceramics, but it's a skill I'd like to develop. Every now and again when I've done an intense stint of steady wheel-throwing, trimming and glazing and I get that nagging feeling in my wrists and elbows and a sore back I realize that my body has limitations. I can't always do it all. And yet, the work doesn't just make itself.
I got into slip-casting last year when I had a master mold-maker make a mold of a bottle vase form that I'd been wheel-throwing and then altering for a while. It was an investment to get someone else to make the molds for me, however, the molds that he made were... perfect. With barely a seam to clean up, and with the prototype being exactly 12% (shrinkage rate) larger than my original, it was a good intro to slip-casting for me.
I've been wrestling with the idea of making other molds, for instance, making my mug designs into a mold, but I can't really get over the lack of throwing lines on the inside of my mugs that wouldn't be there in a molded mug. There is something about holding a mug and seeing the hand of the maker and the process that I get all nostalgic about. Being that I feel so strongly about the work of mine that would be handled the most staying the most hand-made, I decided to give some slip-casting on a 'mini-series' or a little grouping of vessel forms that are outside of my regular work a try.
So here's the start of this process- I'm working on a little set of dishes for my kids- and most likely other kids out there once I work out the kinks. A small plate/bowl/cup, all 1 part molds to keep things simple and stackeable. The molds above are the handle and bowl, I'm working on the plate and then cup over the weekend. The molds all have to dry out before I'll be able to tell if they worked, but it feels like a good place to start.
About the process: I used a broken plastic sheet from a flourescent light as the forms around my mold. Basically I used clamps to keep it 'round' a plastic bat or base. You have to seal the seams with clay so the mold won't leak when you pour in the plaster, but the pattern of the plastic make your mold look real pretty! This idea is great for 1 part molds but L shaped forms are best for 2 or more part molds.
To make 2 or more parts to a mold, you can use "Murphy's Oil Soap" brushed onto the plaster approx 3 times (letting layers dry in-between) so the plaster doesn't stick to itself. I also cast an 'overhang' top- no technical terms here, but a portion that allows the slip to stay above the lip when I'm pouring it in. I cut off the excess with that top part on and it allows my lip to be even and nice.