Saturday, March 6, 2010
Preparing a new plaster mold (Part 2)
I've lifted the first large side piece from my mold, so now I can start removing the inner pieces. The first one that comes off is the handmade neck-and-shoulder insert, since it partially covers both the ear piece and the first front leg piece.
Pieces are designed to be removed in a specific order, and to be pulled in a specific direction. For this one, it pulls upward and slightly to the right. (If it could have been pulled straight upward, there wouldn't have been a need for an inner piece, and the head and neck would have been included on the large side piece.)
The dark areas are where the slip seeped out the seams. This tells me that I mixed my slip a little too thin for this particular mold. I also have just a little bit of clay scraping on the forelock, so I trim those areas. The clay that seeped is cleaned off with a soft makeup sponge.
This is a good shot showing why the first casting isn't used. The white areas along the jaw, lower neck and shoulder are from the mold release. It usually takes one or two castings to remove the film the release leaves behind.
The next inner piece removed is the one between the ears, which I often call the "hat". Unless a horse has mane obscuring the ears, he always gets a hat. It pulls perpendicular to the ears, and this has to be done with care since it is really easy to take an ear off.
Each time I remove a piece, I am checking it for any areas where it is scraping off a layer of clay. When I find them, I use the hook tool to carefully trim the plaster flashing. Once the pieces are cleaned of any excess clay, the are reassembled alongside the other half. This is especially important with minis because the mold pieces are often small and easy to misplace. Once the mold has dried, pieces cannot be repoured, so a lost piece is a ruined mold.
Usually at this point, there are a number of options for removing the horse. Some separate out from the other large side piece, balanced on the remaining inner pieces. Sometimes a few of the leg pieces pull out first, then the horse and remaining inner pieces pull from the large side. Finn was designed to pull with all four gusset pieces still attached to the casting, but it turned out that the two front gusset pieces will fall off freely without removing him.
If I had been smarter, I would have seen this and designed the frontmost gusset (encompassing the chest and part of the front legs) as a "slider" that pulled away without lifting. As you can probably see from this and the previous pictures, there is an unfortunately placed mold key sticking up in the way. That's because I didn't realize this would work better. Molds are always like that; you see better ways after you have worked with them for a while. Even so, the front gussets on Finn tend to fall free with a little helpful wiggling.
That's good because the next part involves freeing the rest of him from the other side piece, and having his entire chest area to leverage makes that a lot easier. And anything that makes that part easier is a good thing, because it's the place most castings are lost. I'm going to lose this one on purpose, just to show why that is. (He is unusable as the first anyway, so he might as well serve as an object lesson.) I'll explain that in the next part.
at 11:33 AM