Prop-Rageous

Hot Glue Casting

The "Problem"
We didn't actually have a problem, here so it was more of a hypothetical problem. The premise is:

What do you do if you realize you need a flexible casting today, and you don't have access to traditional casting supplies and you don't have time to wait for them to be delivered?

This project really came about because I had some time on my hands and was looking for something to do. It wasn't because I needed it, rather I needed to see if I could do it. I have cast hot melt glue in silicone molds before, but I wondered if you could mold in hot glue and then cast hot glue into it. My colleagues, Ainsley Furgason, Mason Wynder and I purposely did not look to the web or anywhere else to see if this had been done before. This project was intended to be a Tabula Rasa kind of project.

I know some people in the industry who hate hot melt glue. They think it is a tool that is beneath the dignity of the craftsperson. My thought is that hot glue is just another tool. You wouldn't say to a hammer, "Because you are not a screwdriver, you are not a tool." No, you would keep it in your toolbox and bring it out when you needed a hammer. I feel the same way about hot glue.

Project Goals
*Create a mold and a cast from non-traditional casting materials one would normally find in a scene shop.
*If the cast was flexible, that would be a bonus.
*Succeed or fail, blog about it.

The Process
Obviously, the first step is to find an item to mold and cast. Naturally, I found a plastic Halloween costume belt buckle in the shape of a skull and crossbones. Naturally.

Plastic belt buckle

The "hardware" has to go

The buckle part of this plastic bit needed to be taken off, so we used a Dremel Tool to grind it off.

Removing the unwanted plastic clasp

Mission accomplished

The next step was to build the box for the mold. Remember, the point of this exercise was to use non-traditional things you might find in a scene shop.

The box was made from a square of MDF that was larger than the skull. We attached the skull to the MDF with Super 77 spray adhesive. The sides of the box were made from paint stir sticks we had just lying around. We cut them to length on the chop saw and taped them in place with painter's tape.

Scrap of MDF

Super 77 spray adhesive

Skull attached to MDF

Stir sticks

Eyeball measuring with a screw for a scribe. Really going old school on this one

Green painter's tape. Blue probably would work

Ready Freddy

Tape wrapped around the backside

We made scribe marks on the mold box walls to give ourselves a high glue mark. To do this we set a Sharpie Pen on top of the skull and scribed a measurement on a craft stick. Then we transferred this mark to the walls of the mold box. We figured the thickness of the Sharpie Pen, resting on the skull would give us the thickness of glue we needed at the bottom of the mold to have an intact casting.

Measuring on a stick

Transferring the measurement to the mold box walls

Done

A mold needs a mold release, and so in keeping with the theme of materials found in the shop, we used WD-40 and gave it a pretty thick coat.

WD-40

Sufficiently slimed

Apparently WD-40 is toxic in California. Who knew? Good thing I live in Idaho

So now we have a problem. We want to mold in hot glue and cast hot glue in a hot glue mold. Seems like hot glue might stick to hot glue. All problems have a solution though. Part of our planning for this project was that we would make the mold of High Temp hot glue and do the cast in Low Temp hot glue.

As we began filling the box with hot glue, it became apparent that our box was too big and it would take forever to fill it with melted glue. Around the edges, we filled the space with un-melted glue sticks to take up room and facilitate filling.

Hi temp hot glue

Un-melted glue sticks

on four sides

Then this happened.

The waiting

is the hardest

part

The glue solidified but was still hot to the touch. That much melted glue holds the heat for a long time, so we broke the walls of the mold and sped up the cooling with a secret weapon.

Peeling the walls back

The secret cooling weapon

We de-molded the skull using sophisticated pocket knife technology.

Knife work. Might be illegal in some countries

Moment of truth

Popped right out

The paint stuck to the mold

As you can see, a pretty faithful replication

Now the tricky part. How do you cast hot glue into hot glue. The moment of truth was upon us. Low temp glue drizzled into a high temp mold. The first thing, obviously was to coat the mold with a generous coating of WD-40, again. Then using low temp glue we dribbled the glue into the mold, making sure to hit the areas with the most detail and relief first and then back-filling behind.

More Idaho safe WD-40 not approved for California sale

Low temp hot melt glue gun

Filling the details first, then back-filling

We noticed that the lower temp hot glue didn't level itself as well as the high temp. That was unexpected but not surprising. So we used a utility knife to shave the raised parts off so it would be level with the mold.

Then the next moment of truth. Would we be able to de-mold the skull? Or would the cooler hot glue stick irrevocably to the higher temp hot glue? Did we waste our time and blow an afternoon? or was this going to work...?

I need a shave

It appears to be working!

It worked!

This image doesn't show the amount of detail that was achieved . From left to right: Original buck for molding, the hot melt glue mold, the finished casting.

The image above doesn't show the amount of detail we were able to achieve with hot glue. The indents between the teeth are visible. Most of the detail transferred. It isn't a perfect cast, but it's really quite good considering the non-traditional way in which we did it.

So what is the point of this?

If you have access to Smooth-On or other products, this would be a colossal waste of time. But if you were getting ready for tech week and needed a casting today and didn't have access to the Smooth-On or had to order it in, this could make sense.

Because it is made of hot glue, the casting is flexible and could be applied to a curved surface. I know there are many traditional products that produce a flexible casting as well. As I said, this is a project that assumes you don't have immediate access to those materials.

So, if I had to do it over, I would create a smaller box for the mold. This would be less wasteful of both time and product.

There is paint transfer from original to mold to cast. I don't know what to do to mitigate that or if I even care to do so.

Eventually, when I am able to go back to work after the shelter at home order is lifted, I will paint the casting and post the picture as an addendum to this blog post.

The results of this experiment were encouraging and given the right circumstances I would do it again.

The Steer Skull

Richard Clifford asked me to craft a steer skull for the set dressing for his set design of You Can't Take It With You. I have never had the opportunity to work on that show, and didn't have an assignment on our production of it. I am at that point in my career where I probably won't have another opportunity to work on this show, and Richard knew that. I think that's why he asked me to build this prop. Plus, skull.

Step 1: Research
I did a quick search of longhorn cattle skulls online. I found images of skulls and printed them off. I also searched for dimensions of longhorn skulls and found that the average longhorn skull is 49 cm long by 21 cm wide by 26 cm high. I don't work in metric so I converted the measurements to imperial rule. The average skull is 19.25 inches long by 8.25 inches wide by 10.25 inches in height. The 10.25 inches included the bottom jaw which I was not going to include in my skull. I adjusted the height to reflect the upper portion of the skull without the bottom jaw.
Time: 30 minutes

A couple of research photos with layout lines

Step 2: Layout
I acquired a block of polystyrene bead foam from the local farm store. It was a block of foam that had been used in a freight truck to keep loads from shifting. It was roughly 19" X 12" X 12". I took it to the bandsaw and set the fence for 4" and cut the block of foam to the appropriate size.

Then I drew layout lines on one of the images and then scaled and transferred those layout lines to the block of foam. Once I had the registration lines in place, I then cartooned out the top of the skull and the side of the skull on the foam block.
Time: 30 minutes

Foam block. Spray can in image to establish scale

Cutting the foam block to size

Sized

Layout lines scaled from the layout lines on the image

The cartoon of the top of the skull

The cartoon of the side of the skull

Step 3: Cutting the Blank
I first cut the top of the steer skull on the band saw, being careful to cut each side in a single pass. As I cut the sides, I saved the cast off pieces. When the two top cuts were completed, I reassembled the block of foam and taped it back together. This was done to facilitate cutting the side of the skull.

The results of this cutting technique was a compound shape cut on the bandsaw that formed the blank that was now ready to be carved and detailed.
Time: 15 minutes

Cutting the top of the steer skull

2nd cut on the top of the skull

Sides come off in whole pieces

Reassembling of the foam block with blue painters tape

Cutting the side of the skull

2nd cut on the side

The blank just before the reveal

The skull blank revealed

And on it's side

Step 4: Carving
I roughed out the blank with two different sizes of surform tools. Then I cut the deepest part of the relief, the eye sockets and the space in the skull immediately behind the eye sockets with a Dremel Tool. I also used the Dremel to put the finishing detail on the rest of the skull.

I carved the teeth with an old soldering iron. I used the entire length of the soldering iron for the teeth, rather than just the tip. I wanted to use the soldering iron because the heat of the iron would cause a smooth skin on the teeth of the cow skull and would help give a better final finish.

When the carving was done, I cleaned it up with an orbital sander.
Time: 45 minutes

Surform tool

Smaller surform tool for finer work. Notice the research material in the foreground

Rough carving

From the side

Detail with the Dremel

Eye socket in

Soldering iron for detail

Using the length of the soldering iron

The teeth

Bottom of the teeth

Orbital sander

Smoothed over

Top view

Other side

Step 5: Carving the Horns
I have used pool noodles for crafting for many years. They come in various sizes and shapes. Pool noodles are flexible, but hold their shape very well. They are also cheap. The downside of pool noodles is that they are made of polyethylene. It is very difficult to find a paint product that will stick to it.

From the beginning, pool noodles seemed to be the best solution for the horns in the longhorn skull. I bought a couple of pool noodles from the dollar store. I matched the hole in the pool noodle to a 7/8 inch dowel. It was a snug fit. Pool noodles usually are about 4' long, and I knew I would not be using the entire length, but at this point I was unsure how long the finished horns would be, so I decided to work on the pointy end first and cut them to length when I had more information.

I marked an arbitrary taper on the dowel and then continued the taper on the pool noodle. When I had what I considered to be the right taper, I headed to the shop and the belt/disc sander.

I sanded the cone shaped taper into the dowels first, then I cut the dowels to be about six inches in length. Then I cut a small dowel about four inches long and inserted it into the end of the pool noodles. I did this to provide a rigid core to sand the pool noodle around.

When I put the dowels and the pool noodles together, there was a small ridge between the pool noodle and the dowel, but I considered that would be okay because even at this stage I had decided to even that out with a coating of Fiberglas.
Time: 15 minutes

Arbitrary taper marked on dowel and pool noodle

Shaping the dowel. Notice the safety glasses.

Measuring for a cut

Completing the cut

The temporary dowel

Inserted

Shaping the pool noodle

The ridge.

Temporary dowel removed and the permanent dowel fitted.

Step 6: Creating the Stand
I decided to create a wooden base for the steer skull that would be integrated into the skull itself and would provide a sturdy support for the horns. I wanted all the weight of the horns to be carried on the stand, rather than the polystyrene skull. The block of foam I had was medium density polystyrene and therefore not particularly robust.

I found a couple of scraps of 1X3 and began eyeballing my measurements. I did this by comparing them to the carved foam skull. When I was satisfied that I had it right, I cut the boards to length and shaped the top board on the belt sander. The top board would be the one that would fit just under the top portion of the skull.

When the pieces were finished, I screwed them together. Finally, I cut a 14" section of the dowel for the support for the horns.
Time: 15 minutes

Eyeballing the measurement

Marking

Marking the curve

The curve

Shaping the 1X3

verifying

Setting on the base

No technicians were harmed in this process

The stand

Cutting the dowel to 14 inches

Step 7: Attaching the Horns
I took a 7/8" spade bit and drilled a hole in the skull where the intersection of the horns would be. I had to drill it from both sides because my spade bit wasn't long enough to bore the hole all the way through.

I then marked and cut the spot with a Dremel where the stand would intersect with the skull. When that was complete, I placed it in the channel and marked where the dowel would go. Next I drilled the 7/8" hole in the wooden stand.

Then came the moment of truth. Would everything fit? Since this part was all eyeballed, there was a chance it wouldn't work. luckily, though it did. It all fit together nicely.
Time: 15 minutes

Drilling the hole

Marking the spot for the stand to rest inside the skull

Made a decision then changed it

Cutting it out with the Dremel

Final fitting

Marking the stand

Drilling the stand

Moment of truth. It fits!

Step 8: Final Horn Assembly
I decided early on to use coat hanger wire to shape the horns. I like to craft with coat hangers because they are cheap, they are everywhere, and they are made of stiff wire. I figured I could use coat hangers to help keep the shape of the horns.

I decided each horn would need four coat hangers. I selected eight hangers and began cutting the hook off, then straightening them and finally cutting them all to approximately the same length.

Next I made drilling marks on the dowels at the skull and at the end of each horn. Then I put a piece of tape as a marker on my drill bit as a depth gauge.

After the holes were drilled, I began the wire and dowel assembly by using Gorilla Glue. Then I realized I was too impatient to use Gorilla Glue and abandoned it for hot glue. That being said, I like Gorilla Glue and I use it often. I was just in a hurry on this project.

When the wires were attached, I eyeball measured the pool noodles and cut them to length with a bread knife. Then I sleeved the pool noodles over the wire and dowel assembly.

Finally, I drilled a pilot hole in the frame and the main dowel and then drove a drywall screw in to hold the dowel in place side to side and to keep it from rotating.
Time: 45 minutes

Wire coathangers

Cutting off the hook

Hookless

Straightening

Raw material

Cutting to length

Depth gauge

Marking

Drilling

Gorilla Glue

Nah, I'm going to hot glue that. Are my hands really that pink?

Wire and dowel assembly

Marking the pool noodle

Cutting the pool noodle with a bread knife

Assembly

Very large steer horns

Securing the dowel

Step 9: Adjustments and Mastic
Richard had asked for the skull to be about 3' wide. At this point the skull was closer to seven feet wide. I knew I'd lose some of the width by bending the horns, but I also knew I couldn't bend them enough to make them look good and get close to the measurement he was asking for.

I contacted him and suggested the horns would probably be wider than 3'. He said the wall they were going on was about five and a half feet wide. I settled on about four and a half feet wide for the finished width.

Then I disassembled the horn rig and cut about a foot off of each wire and re-glued them. In order to do that I had to clean off the original hot glue, which was gumming up the holes.

I measured the pool noodles again and re-cut them. Then I sleeved them over the dowel and wire assembly one more time. The new width was far more reasonable. Then I bent the wires inside the pool noodles and formed the horns as symmetrically as I could.

When I was satisfied with the bend of the horns I applied Rosco Flexcoat as a mastic. I needed to use mastic on this project because I needed a barrier between the foam and the fiberglas resin. Fiberglas resin will eat polystyrene foam.
Time: 30 minutes

Shortened horns

Final bend and applying Rosco Flexcoat

Mastic finished with a can of Rosco Flexcoat as a shameless plug

Step 10: Fiberglas
I had never used fiberglas before this project. I had used fiberglas resin, but had never used the actual glass. I found two different types of fiberglas mat, one that was a woven fabric and the other that resembled Chaos Cloth from Rosebrand. I chose the Chaos Cloth lookalike. I figured it would conform to compound shapes better.

I had a friend there who walked me through the basics of fiberglassing. First I cut the mat into smaller more manageable pieces. Then I used Super 77 spray adhesive to attach the glass mat onto the steer skull and the horns. I was especially careful to make sure that the pieces that wrapped around the top of the skull spanned the attachment joint between the skull and the horns.

When I had the skull all wrapped in glass matting, I began mixing and applying the fiberglas resin. I used a silicon basting brush to apply the resin. I learned that tapping the resin in place was more effective than trying to brush the resin in place. When you brush it, the mat tries to move around with the bristles. The next time I use fiberglas, I will find a way to attach the glass mat a little more securely. It was a little frustrating when it moved around and I had to do considerable cleanup work with it after it cured. Once I had all the resin on the skull, I went home. There was nothing I could do on it until the resin cured.
Time: 1 hour

Cutting the Chaos Cloth lookalike

3M Super 77

Glassed

Closeup

Adding resin

The fiberglassed skull

Step 11: Cleanup and Paint Prep
The fiberglas did everything I hoped it would. It created a hard shell on the skull and it secured the pool noodle horns in place. Prior to the fiberglas, the horns still had a tendency to flex and bounce. The fiberglas fixed that.

There were downsides to the fiberglassing as well, though. Since it was my first time, and I had been in a bit of a hurry, there were places where the glass mat hadn't laid down very well. There were also places, especially around the eye sockets where the ends of the glass mat hadn't been covered with resin. Those areas needed to be trimmed. For this I used my Dremel Tool with an aluminum oxide grinding bit.

Since I was grinding fiberglas and resin, I wore safety glasses, a particle mask and gloves and I worked in the fume hood.

When the grinding was finished, I used a tack rag, which is essentially a piece of cheesecloth with sticky resin infused. Tack rags help to remove dust from a piece in preparation for paint.

I also painted an ivory color inside the eye sockets and a few other places where I felt the polystyrene was unprotected. I did this because my intent was to spray paint the skull. Polystyrene foam melts under the influence of the solvents in most spray paints.

While that was drying, I changed the bits on my Dremel Tool to a small diamond point bit, and carved the bone plates in the surface of the skull.
Time: 45 minutes

Grinding the rough stuff with the Dremel

Closeup of eye socket

Tack rag

Painting inside the nasals and the eyes

Cutting the bone plates into the skull

Fabrication complet

Step 12: The Paint Job
I am a big fan of Design Master Color Tool in prop building. I used Ivory for the base of the skull and Almond for the base of the horns. Then I applied green frog tape to mask the skull from the horn paint job.

The horns were painted with a combination of Glossy Wood Tone, Walnut Wood Tone and Chocolate. I wanted the horns to be a little variegated as they were in the research I had found, so I started with the lightest color and worked to the darker colors. When I got to the Chocolate, I used a potato scrubbing brush and dragged it through the wet paint.

At the end, I added Deep Blue in the darkest parts of the horns for depth and richness.

Then I went to old fashioned brush paint for a little aging on the skull itself. I used a Rosco Off Broadway, Raw Umber wash and wiped and daubed it away so the paint would settle into the deepest recesses of the bone plate joints in the skull.

For the last step, I painted the teeth of the skull with white nail enamel.

And then I turned it over to the Properties Department to be hung on the set.
Time: 30 minutes.
Total Time: 6 hours and 30 minutes