Tag Archives: silicone rubber

Video: One-piece silicone block mold

Video: One-piece silicone block mold

You may have noticed I did not post much last week, and that this blog has become a little more sporadic over the past few months. Well, there is good reason for that. Last Thursday, my wife gave birth to our first son. It’s the best prop we’ve ever made.

Speaking of props, I shot a quick video on making a one-piece block mold from Alumilite QuickSet silicone rubber (the kind you can pick up at many hobby chain stores) that I’ve been meaning to put up. It’s not pretty, but it shows off the basics and gets the job done.

Links for the Weekend

Here’s a story about a prop master who has found a new career killing zombies. I think most props people imagine they would be pretty well equipped to fight zombies.

Adam Savage (of Mythbusters fame) has quite an intense and detailed tutorial on making a silicone rubber mold with a plaster mother mold (or as he calls it, a “hard shell mold”). It is perhaps a bit more involved than most theatrical prop shops would ever need, but a lot of the extra steps he does are to keep the mold from collapsing on itself and to ensure the two halves are lined up perfectly.

What do you want to know about drill bits? How about everything! Ok, so this free PDF guide to drill bits deals only with woodworking (no metal or plastics), but it is still a useful amount of information available at a glance.

This is kind of cool. A classmate of mine from undergrad wrote a play a few years ago called The Love of Three Oranges. One of the productions of this play is documenting the construction of their set and props on a blog.

So, I’ve talked about the invention of the jig saw before; its history is at least somewhat intertwined with the history of fret and scroll saws. Well, Chris Schwartz has a piece on the history of the coping saw, another tool sharing this history. I personally love my coping saw, and consider it one of the indispensable tools in my prop-making bag.

Mixing the alginate

Lending a Hand to Titus

Our last show of this calendar year was Titus Andronicus, which, depending on the budget, could be a prop person’s dream or nightmare. Meghan Buchanan was the prop master on this show, and her company, Paper Mâché Monkey, was handling most of the acquiring and construction of the props. Since King Lear was winding down, I offered to lend a hand, and as luck would have it, they needed a hand. Jay O. Sanders hand, to be precise; after he cuts it off, it shows up in a later scene.

Mixing the alginate
Mixing the alginate

Life casting a hand is one of the easier parts to do; the only tricky part here was that they were rehearsing uptown at Second Stage Theatre and I only had an hour, so I had to prep everything beforehand so I could be in and out like a ninja hand caster before anyone knew what had happened.

Jay O. Sanders molding his hand
Jay O. Sanders molding his hand

I used alginate because it’s cheap, non-toxic, safe on the skin, and sets up quickly. It’s made from seaweed and used in dentistry to make molds of your teeth and gums. After mixing the powdered alginate with water and filling a hand-sized container, I asked Jay to pose his hand and submerge it. It doesn’t heat up like plaster; it just slowly thickens. In about ten minutes, it had solidified enough to where Jay could remove his hand. It’s stretchy enough that he could pull his hand out without breaking or tearing the mold (if done slowly), and it doesn’t really stick to anything (no mold release is needed). The little bit that does stick can be washed off with water.

Pouring plaster in the alginate mold

The thing with alginate is that it starts shrinking right away as it loses water. You only have about two or three hours to make a cast before it has shrunk noticeably. I mixed up some plaster while still at Second Stage and poured it in. After it had hardened enough, I packed up my stuff and took the subway back down to the Public Theater.

Plaster hand inside the alginate mold
Plaster hand inside the alginate mold

Now I could just tear the alginate away until the plaster hand was free.

Brush-on mold
Brush-on mold

I decided to do a brush-on mold for this because of the shape of the hand. I had only attempted a brush-on mold once before and it didn’t go so well. This time around was only marginally better. I ended up making it work, but that’s about the only good thing I could say. After the rubber mold set, I built a two-piece plaster shell around it for support. I ended up having to cut open some of the silicone mold to remove the plaster hand inside.

Unpainted silicone rubber hand
Unpainted silicone rubber hand

I cast the hand itself out of Smooth-On Dragon Skin, which long-time readers may remember being used in both the dead body and head for The Bacchae, as well as the dead lamb for Little Foxes. Dragon Skin itself cures fairly translucent and colorless, so I tinted the whole mix with a flesh color. I also embedded some dowels inside to cut down on the amount of silicone rubber I would need and to act as bones.

Hand of Titus Andronicus
Hand of Titus Andronicus

I “painted” more Dragon Skin over top, tinted with different colors. I rubbed some darker colors into the cracks and crevices to give it a bit of depth, and added a bluish tint onto the veins. I was using a fairly thick mix so it wouldn’t run. Silicone rubber is self-leveling unless it is thickened, and it can be pretty glossy if allowed to do that. I didn’t want that on the hand, but I took advantage of that for the fingernails, where I used a pretty thin mix and only a touch of color to get a shiny and translucent effect.

"I kind of feel like that kid who found the severed hand..."
"I kind of feel like that kid who found the severed hand..."

The hand has gone through some changes since I took these pictures; the bones on the back were cut down in length, and a lot more blood was painted on. All told, it only took about three days between them asking me to lend a hand making a cast of a hand to the cast having a hand in hand for rehearsal.

The Prop Builders Molding and Casting Handbook

Review: The Prop Builder’s Molding and Casting Handbook

The Prop Builders Molding and Casting Handbook
The Prop Builder's Molding and Casting Handbook

In Thurston James’ second book, he tackles the subject of molding and casting for prop makers in more detail. The Prop Builder’s Molding & Casting Handbook guides you through the most common materials and methods used in many prop shops. Because of its specific focus (and better organization), this book is far more successful than his previous Theatre Props Handbook, which, as I mentioned in my review, meandered through disparate topics with no way to quickly find information.

Though written in 1989, the methods described in this book still hold true today. Though the range of materials we can use today have grown dramatically, they remain improvements and new formulations to older materials whose predecessors can be found in this book.

It remains one of the most widely recommended books for molding and casting props because of the unique niche it fills. It describes the most common materials and methods used in props shops and by hobbyists; these materials are used because of their cost, ease of use, availability, and proven results. Books on molding and casting for manufacturing and industry are more focused on specific or specialized materials, and they aim for a level of consistency and cost efficiency which the prop artisan would never possibly need. Shaving a tenth of a cent off the cost of a casting makes a difference if you are casting ten thousand pieces, but it will be impossible to notice if you are only making ten.

James seems to have had an epiphany in shop safety between this book and the last, as he now presents clear and accurate safety precautions in the beginning of the book, and continues to reiterate them throughout. In his Theatre Props Handbook, safety precautions were nearly nonexistent.

The book does a good job of covering the generalities of mold making and casting. It discusses the model and its preparation, and defines a number of necessary terms, such as undercuts, release agents, mother molds and the like. It describes the considerations of making a mold of your specific piece, and breaks the various molding materials and casting agents into categories. In a way, it describes the process of choosing your materials in an almost flowchart-like manner. If you know what your model looks like, and you know what kind of properties and appearance your castings need, then you can narrow your choices of mold material and casting material down to a few choices. In the book, he describes over thirty of these material choices.

The bulk of the book is used to guide you through the specifics of working with each of these materials. Specifically, he talks about plaster, alginate, latex rubber, and silicone rubber (RTV) mold-making. The casting materials he describes include latex, neoprene, papier-mâché, Celastic, fiberglass (GRP), hot melts (such as wax, plasticine, hot melt glue and hot melt rubber, breakaway glass, thermosets (specifically polyester resin), water-extendable polyester, and urethane. He also has a section on casting with hardware store products, like caulk, autobody filler, water putty, and several others. Finally, the last section of the book describes vacuum forming and how to construct a vacuum forming machine.

Weigh out the silicone

How to make a breakaway telephone

One of the trick props we needed for The Book of Grace was a phone which John Doman smashed during every performance. We decided that the phone receiver would remain real, but the part it hung on would be cast from plaster. It would all hang on a wooden base, and a collection of “phone innards” will be held inside the plaster part, so when it broke, an assortment of metal bells, chip-boards, and other electronic components would be left hanging on the wall.

Weigh out the silicone
Carefully weigh out the silicone

We made a two-part silicone mold of the phone. Making a two-part silicone mold is beyond the scope of today’s post. However, I did get a photograph before the pouring of the first part. At this point, Natalie Taylor Hart took over the project.

Preperation for making a mold of the phone
Preparation for making a mold of the phone

Normally, the next step is to make the second half of the mold from the back of the phone. In this case, the shape of the back was far more complicated than what we needed, and we were worried the plaster cast would be too thin. So we took the first part of the mold and built up the thickness we wanted to achieve out of Klean Klay. The Klean Klay is the yellow substance in the photograph above, and remains flexible like plastiline. It also does not contain sulphur, which reacts with the silicone mold-making compound. The mold still needed some tweaking, so Natalie carved directly on the silicone to perfect it.

A view of the mold
A view of the mold

We wanted the color of the phone receiver to match the back part, which was the sort of taupe that most appliances from the late twentieth century came in. When the plaster phone gets smashed, the broken edges would show up white. Thus, we needed to dye the plaster while it was still in liquid form. Natalie found that a tablespoon of Rit tan dye in the mix made the best color match.

Adding dye to the plaster mix
Adding dye to the plaster mix

Natalie sifted the plaster into the water until tiny islands of plaster began to form on the surface. Once she had made a few phones, she had the exact measurements of both plaster and water marked down.

Combining the plaster into the water
Combining the plaster into the water

Next, she let the plaster sit in the water for about 30 seconds. “Wetting” the plaster allows it to mix more thoroughly.

Letting the plaster wet up
Letting the plaster wet up

With such a small amount, she mixed it by hand. This also gave her a tactile way to ensure all the lumps were worked out of the mix.

Mixing the plaster
Mixing the plaster

Natalie discovered the best way to pour this particular mold was to slosh plaster over the top half before putting it together. It was important to get plaster in all the cracks and crevices or the strength would be compromised.

Pouring the plaster into the mold
Pouring the plaster into the mold

The phones set up overnight, but they actually took two to three days to fully dry. We could not get any kind of adhesive to keep the plaster parts onto the bases until all the moisture was completely out. We ended up needing around 40-50 phones for the run of the show, but since we could cast more than one a day, we could make them throughout the run rather than all at once.

Phones
Phones

Finally, here’s a video showing the end result. This was taken earlier with a different phone model, before they changed it to the slimmer model.