Tag Archives | production molds

Evolution of molds

Or, “Why There are Fewer Custom Glazes Out There Now”

When I was first learning to glaze, my good friend and mentor Joan Berkwitz generously offered to send me a handful of old Pour Horse production molds. These allowed me to experiment with underglazing without fear of ruining an expensive bisque, which was a godsend. They also allowed me to learn to pour slip and clean greenware with what were some very forgiving molds.

But their true value came when I began to make my own molds. Nothing teaches how molds work like getting castings out – or not getting them out, as the case sometimes was! They also allowed me to see how Joanie solved mold-making problems. Although I rarely make castings from them anymore (some are truly worn out by now), I still use them in this way.

I had a bunch of them out the other day, weighing potential solutions to some of the challenges presented by Elsie, and it struck me that it might be fun to share a visual of just how far mold-making has come in the last decade. I took exploded views of three different mini-scale molds. All three were designed by Joanie, though the production copies of the middle one (Finn) were made here at Blackberry Lane.

This is “Limerick“, which I believe was the second Pour Horse “thumb scale” release following the Shetland mare, “Bressay“. Her mold is only three pieces: right side, left side and the ear hat. (Not only did I learn to pour slip with this mold, but I also learned that you don’t clean a messy mold with a wet sponge. That’s why the one side is discolored!)

The early minis like Limerick were designed with production in mind, so the sculpture was simplified. The hindquarters, for instance, were “diapered”. That is, the whole area between the two legs and under the tail was filled in. Once ceramic producers started getting working with sculptures designed for resin casting – with their detailed fannies, chests and “boy parts” – molds had to have gusset pieces. Turned heads also added mold parts. This is “Finn” with eight pieces: right side, left side, ear hat, head/neck piece, two front gussets and two back gussets.

This is now pretty much the standard mold design for what I think of as an easy piece.

That’s because we now make things like this. This is the three mold set for “Taboo” with a total of thirteen pieces. His three separate molds cast (top to bottom in the picture) his 1) head and tail, 2) one front and one back leg and 3) the rest of his body and legs. There are also numerous small pieces for the undercuts in this mane and tail, all handmade with each new mold. His various pieces are cast and then he is assembled while the greenware is still damp.

Needless to say, there are a lot fewer Taboos (and Vixen, who casts from a similarly complex set of molds) than Limericks out in the world! But each mold is pushing the envelope for what we once thought was possible in earthenware.

Which brings me to Elsie and Oliver. Those are two almost-dry Oliver molds off to the right. He is, by present-day standards, a relatively easy mold. I have high hopes that will allow me to get more Olivers out in the world.

The two molds to the left are copies of Elsie’s tail mold. It takes six pieces to make her tail alone – twice as many as it takes to make a whole Limerick. I’m still designing the mold or molds for the rest of her, so I don’t know what the final piece count will be for her. In many ways her size alone makes her easier to do than the minis, though, so hopefully there won’t be a host of motherless Olivers.

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Preparing a new plaster mold (Part 3)

The only remaining pieces (aside from the large side) are the two back gusset pieces, which are tinted pink in this picture. These two pieces are designed to lift up with the casting, with the horse balanced on top like a pedestal. This is the way most horses are removed.

The two front gusset pieces came away really clean, so they didn’t need an adjusting.

But while the first side came off easily and the two front pieces came away clean, the casting was still a little too soft to be considered leather-hard. Normally I would set everything aside at this point to let the casting firm up a little. That’s because to break the seal on the other large side, I’m going to need to rock the casting a bit, and I don’t want to risk collapsing the barrel, shoulders or chest. But since this casting is already lost, I went ahead and tried to remove it to show what happens when a casting is removed too soon.

Not only was my guy too soft to retain his shape as I jiggled him, the clay on the other side was still wet enough that it hadn’t fully released from the mold. That pinned him in at the top if his shoulder and the point of his hindquarter. (You can also see the cloudy film the release residue has created on the surface of the clay.)

Here he is on the gusset pedestal, showing how pulling the casting while it was still pinned to the side pieces caused the piece to rip apart.

The two bits of stuck clay show where the casting had not yet dried enough to release from the mold. Fortunately it was the clay that was too damp, which is relatively easy to clean up with a fine (dry!) sponge. If the mold itself had still been damp, it might be impossible to completely clean the clay from the mold. Patience really is one of the most important qualities in slipcasting!

Even though my casting was badly damaged, I was still able to wiggle the two back gusset pieces free so that I could check for flashing. Sure enough, both hind legs had scraped clay showing where I needed to correct the molds.

It’s hard to believe that a casting like this is a success, but it was because I was not after a usable bisque. What I wanted was information, and this first casting provided it. By looking at how the casting was going wrong, and adjusting the mold pieces accordingly, I was able to fix the mold so that future castings were easy to get.

Here is the second casting from that same mold, poured to double-check that I caught any potential problems. As you can see, the mold is clean and he came out whole, so I can declare this a working production mold.

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