A silicone master mold is an obvious safety net in glass casting: If you accidentally employ one of the 10,000 methods for destroying a piece during casting, a master model gives you a second chance.

vintner sculpture-original

The original sculpture (and photo it was taken from). It measures about 14×14 inches, and maybe 5 inches deep.

That’s not all, though. As tedious, time-consuming, expensive and messy as they are to create, master molds are probably the single best investment a glass sculptor can make.

A collection of master molds is also called a parts library. A parts library can contain molds you’ve made of… just about anything:

  • Your sculptures (or parts of your sculptures)
  • Found objects
  • Plant and animal parts
  • Lifecasts
  • Dishware
  • Common shapes (cones, hemispheres, etc.) that you use often

Once you have one, a parts library lets you cast a quick wax (or clay) of a common element in your work, then modify and incorporate it into other things.

For example, I sculpted this clay portrait (right) of woman I met at a farmer’s market, then made a silicone master mold from it. Since completing the pate de verre sculpture, parts taken from that mold have made appearances in several other pieces where the face is subordinate to other design details:

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Urethane face mold

But my parts library also includes molds made solely for components I can use in other pieces. One such is the urethane face mold I made maybe 10 years ago.

I frequently tuck small faces into larger sculptures, and I always put a face into my cast pendants. I got tired of forming yet another face with every sculpture, so finally made the mold at right.

By having a ready-made mold with neutral, eyes-closed faces, I can quickly make one (or ten) basic faces for incorporation. They can be cast in wax, or impressed with earthen or oil-based clay, whatever I happen to be working in.

Once made, I can easily modify them for the look I need: Eyes open, mouth speaking, add shoulders and the back of the head, dress with hair, etc.

Faces I’ve pulled from that mold have been the basis (so far) for perhaps 30 different sculptures. Here are a few examples:

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It’s also useful to make silicones of plants and other things that are only around seasonally. The hosta leaves just outside my front door display some amazing textures, and I have perhaps 10 molds of them, in various sizes. I’ve also taken molds of hydrangea, iris, cherry and maple leaves.

The silicone mastermold can be used to make waxes or clays that become new models…or they can become the form you use to make the refractory mold. The “negative” blue mold on the left, below, produces the model; the “positive” purple mold on the right can produce the refractory mold.


I brush wax into the blue mold (left) to create wax leaves that can be incorporated into other sculptures. The purple mold (right) is for making refractory molds; I’ll build layers of refractory plaster over the mold, then gently tease out the silicone. If I put glass into the mold and fire a full casting fuse, I’ll get an exact replica of (only one side) of the leaf.

Functional ware molds

Every so often I hit up the thrift shop for well-shaped bowls, platters, boxes and serveware. Often, they’re not really suitable for slumping molds; if I slump the glass into the top, I will lose the nice footing on the underside. But if I drape the glass over the underside, I’ll miss that nice smooth-top (and the foot will be on the wrong side of the piece).

So…I make a silicone mold of really classic, beautiful dish shapes. Now I’ve got a mold that can produce perfectly shaped wax dishes which I can modify or decorate any way I like.

That’s a big advantage when you’re trying to make a set of dishes, for example; you’ll have the same basic shape underlying each piece. It’s much easier, and makes far more reproducible shapes, than trying to make a new bowl or dish every time. And if you stick with basic dish shapes, you’ll have a nice, neutral starting point for your creative urges, one that won’t look a thing like the original.

These pieces, for example, all started as simple, common chipped plates and bowls from Goodwill.

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waxhemisphereYou don’t have to make everything in your parts library; I also buy interesting silicone ice cube trays and candy molds.

There’s not much point in laboring to produce a perfect geometric shape if I can find what I need in a baking mold, and it’s actually cheaper than making one myself.

The wax hemisphere at left came from a silicone cupcake mold–it’s got a flawless, high-gloss surface, ready for altering.

Hemisphere molds can become full moons, bouncing balls or just about anything with that shape, including cheeks and chins and breasts (don’t ask). This particular one became the base of a goblet.

I could easily build up the base myself, from poured wax…but the one from the pan is already perfect. It gave me a head start on the goblets I made this summer for a friend’s wedding.

wedding goblet

Kat Chalice, about 8 inches high, of Gaffer lead crystal.

Keeping a parts library isn’t difficult; it takes a couple of sturdy shelves, old dry cleaner bags (to wrap the molds and protect them from harm).

How do you start a parts library? The best way, I think, is build a few component molds yourself. It’s not only a great way to get your library off the ground, it’s also a good way to learn some basic master mold-making skills.

So…in the next post (this one is getting too long) I’ll talk about how you get started, and demonstrate some simple(r) ways to make component casting molds.