Having come to this method of making a complex mold through lots of trial and error we figured it might be fun to outline the steps we take with photos. This is one method that we have been using with pretty great success. The mold in this demo is our "mini white" espresso cup the 3oz version of our popular flat white cup. This mold is getting an overhaul to make the finished product more durable in the Cat & Cloud cafe setting. After going through a few different lip designs trying to balance aesthetics with comfort it was determined that we needed to beef up the lip of some cups to increase durability.
1. Make a model, keeping in mind your desired finished size, bisque fire it to cone 06-04.
2. Seal your bisque model after sanding smooth and marking your parting lines (our pencil had really soft lead, not ideal so we had to use care in sealing to keep our lines from smudging.)
3. We start by blocking the whole model in clay except for the foot.
4. Use some mold soap on the foot before pouring plaster
5. Remove the bottom section and clay blocking from your cottles and cut the clay well in front of the parting line.
6. Remove that piece of clay and mark your base and model for alignment. Remove the model and smooth the base with a surform tool and sanding screens.
7. Cut mold keys (we use a demitasse spoon to start the hole then a cupping spoon to shape it out)
8. Replace your model on the base and use the clay you cut to block your model in half.
9. Use mold soap and sealer on the plaster base before securing the bottles and pouring more plaster.
10. After removing your cottles for the second time trim the plaster back to make a nice sharp parting line, then cut mold keys, soap, seal and place back in the cottles.
11. Removed from the cottles these are the first three sections.
12. Use a tool to scrape back the excess plaster around the lip line and smooth out the top of the mold before cutting keys.
13. Since we are making this mold as a master we need it to be pretty. You can see here that we re-poured the bottom and one side section, also we unloaded a kiln!
14. Place a truncated cone on the interior of the lip to create the sprue. Soap and seal the top before cottling and pouring the top section plaster.
15. Here is the completed mold assembled before we cottle the pieces and pour rubber.
16. After pouring our rubber and waiting 16 hours for it to cure we take one more step before removing it from the cottles. Heat any round metal item that looks like it might make good keys in rubber and press it lightly into what is the back of your rubber mother mold. The idea here is to pour about 1" of plaster as a backing for your rubber, by doing this with the rubber in exactly the position that it was poured you don't risk distorting the working mold pieces because you'll always have the rubber supported in the proper position.
Once you have the rubber mother mold you can make as many working molds as you need (not pictured is the rubber pour for the top and bottom sections of the mold, you'll need those as well).
coming soon, part 2, production from slip to glazed ceramic...