Matrix Mold: Owl Mask, Part 4: Silicone

Sarrah Wilkinson - 6/23/2022

In the last blog, I covered creating the mother mold shell for the owl mask matrix mold. In this one, I'll be setting up the mold shell for pouring the front and back halves of the silicone mold itself.

As I mentioned at the end of the last part, I left most of the clay on the back half of the mold shell, as it allows me to place the resin owl mask in exactly the right position so it is 'floating' between the front and back of the mold shell.

The completed mold shell opened up, with the mask placed on the clay from the bottom half of the mold, and clay residue still in the two top halves of the mold.

Then, I build up clay around the owl mask and add in pieces for my pour spout and venting. At this point, I would like to apologize for being a complete derp and forgetting to take a picture of what the whole pour spout and vent system looks like! You'll be able to see the whole thing in a later photo after the silicone is poured, but here you can see at least one half of it, as well as the keys I've carved into the clay.

The resin owl mask in the first half of the matrix mother mold, with a layer of clay around the outside forming half of the final mold cavity.

For the front half of the mold, I completely clean out all remnants of clay, first by peeling the clay out as much as possible with my fingers and with sculpting tools (I prefer wooden tools to metal for this, to prevent any damage to the mother mold.) When I've removed as much clay as possible, I finish up by scrubbing the rest of the clay remnants off using mineral spirits and a firm-bristled brush, like a chip brush.

The empty front half of the owl matrix mold shell.

Here, you can also see where I've used a handheld power drill to drill holes along the mold edge to hold the pieces together, and a few holes in the mold shell itself, which will act as venting for when I pour in the silicone.

The front half of the owl mold shell showing the holes drilled for venting and for bolting the various mold pieces together.

A clear plastic segment of a straw hot glued over one of the vent holes in the owl mask mold.

On the left, you can see what the mold shell looks like from the outside, using screws with wing nuts to hold the pieces of the shell firmly together. The holes that do not have screws in them are for silicone venting. On the right, I use hot glue to attach a short length of transparent drinking straw around each of the vent holes.

A drawing of three moldmaking situations side-by-side, illustrating how a thick, viscous liquid like silicone may cause an air void and how to create a temporary vent which can be capped to allow the silicone to flow into every part of the mold.

This diagram illustrates how the straw vents work. A thick, viscous liquid like silicone may trap air as it's being poured into a mold cavity, especially if there's a relatively thin area. While the air may sometimes bubble out, it doesn't always have a chance before the silicone begins to set. It's best to plan a series of vents to make sure air escapes and the silicone gets everywhere it needs to be. The hole forms a temporary air vent, and the straw keeps the silicone from just spilling out all over the place once it gets to the hole! As soon as the straw starts to fill up with silicone, I cap it with a small piece of oil-based clay.

The front half of the owl matrix mold after it's been sealed and poured with silicone.

Before I pour in the silicone, I close the mold and use screws with wingnuts to hold it all shut, as shown a few pictures back. Here, you can see that I also use clay to cover the two large holes at the top of the mold, the seam between the mold shell pieces, and any possible silicone escape points. Liquid silicone - in this case, Mold Star 30 (another product from Smooth-on) - can sometimes seep through some pretty thin crevices! The clay is great at making the seal airtight and preventing this.

For this particular mold, I also used a pair of clamps to tilt the mold shell a little so the silicone would flow down from the beak area up around the brow and 'horn' regions.

In the photo, you can see that the first half of the dark blue silicone material has been poured. The straw vent holes were capped with clay as they filled up with silicone, ensuring there were no hidden air voids in the mold.

The cured silicone front half of the mold and the clay residue still left on the back half.

The back half of the mold has now been cleaned off and all of the pour spout and vent pieces have been moved over to the silicone in preparation for making the rest of the mold.

The silicone is allowed to cure overnight, then I open the mold back up. Suction between the newly-cured silicone and the clay means those pry points will come in handy here too! And fortunately, because the resin mask has a large enough surface in contact with the silicone, suction will almost always keep it stuck to the silicone too. Sometimes the pour spout and vent pieces will be attached to the silicone too, other times they'll remain stuck in the clay. All of these pieces are moved over to the silicone and the clay completely cleaned from the other side, as you can see in the photo to the right. I use a bit of petroleum jelly as a kind of temporary 'glue' to hold the pieces on the silicone side.

(And as promised, here you can finally see the layout of my full pour spout and vent system, which I make using spare resin pieces, clay, straws, lengths of wire... any material that doesn't inhibit your silicone will work.)

Once everything is cleaned up, I apply mold release (petroleum jelly) to all exposed silicone, then close the mold back up.

Do not, I repeat, DO NOT forget mold release! Otherwise the silicone will stick to itself and you'll have to cut the whole thing apart.

The mold is closed and prepared for pouring the second half of the silicone matrix mold.

The second half of the silicone will be poured down from the top of the mold, in through the gaps around the pour spout and vent.

A pair of support structures made of PVC pipe have been hot glued onto the front half of the mold to allow it to stand upright when pouring the second half of the silicone and when casting.

The mold will need to be upright for this part - and in fact, this upright position is also how the finished mold will be cast. So, at this point, I add a pair of supports to keep the mold standing up properly. The supports are lengths of PVC pipe, attached with hot glue. It's a temporary structure at first, which I'll reinforce once I've cast the mold a couple times and am satisfied everything's working properly.

When everything's set up, I seal all the seams between the mold shell pieces with clay again and pour in the silicone, just like the front half.

The two silicone halves of the mold getting a soapy bath to clean off residue from the molding process.

Once the silicone has cured overnight, I open it all up, use a pair of small, sharp scissors to clean up the silicone edges, and give the new mold a nice scrub using dishwashing liquid to remove any residue from the moldmaking process.

The completed owl mask matrix mold, assembled and ready to cast, shown from an angle.

The completed owl mask matrix mold, assembled and ready to cast, shown from the back.

Here's the final owl mask matrix mold. At this point, I've had a chance to test the mold and am satisfied with how it casts, so I went ahead and reinforced the PVC pipe supports with some FreeForm Air epoxy putty.

Casting the owl matrix mold, shown from above with liquid resin poured in.

I went through over half a dozen types of resin when testing what would work best for casting my matrix molds, and the one I like the best is called Task 9, one of Smooth-on's specialty resins. It's a 1:1 mix ratio urethane resin that cures clear, so I can color it with mixed-in pigments. It has a relatively low viscosity and a lengthy working time, which makes it easy to pour into the mold. The final cast is also incredibly strong and durable! My testing process involves throwing it onto concrete from 6 feet in the air, so when I say strong, I mean it.

On the downside, it does tend to bubble during the curing process, so a pressure pot is an unfortunate necessity. With a pot, however, the casts come out bubble-free and... basically perfect. This is why, despite the lengthy process of making matrix molds, I love them so much and will continue converting all of my other masks.

The liquid resin is colored - white in this case - and mixed, then poured in through the pour spout until it begins to seep up through the air vents on the other side.

The owl mask matrix mold, opened up to show the result of a cast mask inside.

I place the whole mold in my pressure pot at 60 PSI for a little over an hour. It cures faster during the warmer months of the year. After that, the resin is cured enough that I can open up the mold. It's still just a little soft, which makes it easy to remove the pour spouts and air vent sprues.

The open owl mask matrix mold in the background, with a finished white cast resin mask in front.

And with that, we've got a finished matrix mold and a successful cast!

I hope you enjoyed this series on how I go about converting my masks into matrix molds, and it gives you some ideas for how you might want to handle your own molding and casting situations. Or, maybe you are just interested in the process my pieces go through! In any case, it was fun getting a chance to share this process. Go make some awesome things!

Love the owl mask? You can buy one via the link below!

All blogs in this series are linked from the Making a Matrix Mold page.

Owl Mask Blank
$51.00 via Etsy

Categories: Costuming
Tags: converting, matrix mold, mold shell, Mold Star 30, monster clay, mother mold, oil-based clay, owl, owl mask, pry point, resin, resin mask, silicone, silicone mold
Live Date: 6/23/2022 | Last Modified: 6/23/2022

It's up! Low Poly Dungeon Pack Now Available in the Unity Asset Store

Sarrah Wilkinson - 6/16/2022

Well, that was delightfully fast! My Low Poly Dungeon pack passed review at the Unity Asset Store, and is now up and available for purchase! The full pack features 230 FBX models and a total of 294 pre-made prefabs for use inside the Unity game engine. There are static props, activatable animated props, lit props with fire particle effects, decals (like blood stains and spider webs!), and even a bonus music file by my husband Robbie, which you can hear in the demo video.

I've also got a video showcasing all of the individual pieces.

Not sure if it's the right pack for you? I've also put up a free Low Poly Dungeon Lite pack to try before you buy. It features 19 prefabs from the full pack and gives you a great idea of the range of items available.


Categories: Games
Tags: 3d modeling, asset pack, blender, dungeon, for sale, game, game assets, game dev, game development, indie, live, low poly, modular, showcase, Unity, Unity Asset Store, video
Live Date: 6/16/2022 | Last Modified: 6/16/2022

Matrix Mold: Owl Mask, Part 3: The Mold Shell

Sarrah Wilkinson - 6/13/2022

In the previous post, I talked about how to set up the clay structure I use to form the matrix mold's outer shell, or mother mold. In this blog, I'll be creating the shell.

An additional flange of clay is added where the mother mold will wrap around the silicone. A silicone pour spout is added, along with keys.

The first layer of red Epoxacoat over the clay around the owl mask.

On the left is where I got up to last time. Using a chip brush, I apply a layer of a type of brush-on epoxy called Epoxacoat, available from Smooth-on. It comes in a couple of colors, but they act identically aside from their color. I prefer the red, for purely aesthetic reasons! It is important, however, to use a material that is made to be brushed on - normal epoxy resin or polyurethane resin might not stick long enough to cure properly!

You can use a spray-on mold release on the clay prior to applying the epoxy, but I've found it doesn't make a lot of difference - the clay and epoxy will stick to each other quite a bit regardless. I do apply a mold release to the PVC pipe so the epoxy doesn't stick to it permanently. There are several types of mold release you can use, but I typically just stick with petroleum jelly for this - cheap and readily available!

A chip brush with the bristles cut into a wedge shape.

The second layer of red Epoxacoat, colored slightly darker, being applied with a chip brush.

Here are a couple of useful tricks.

First off, to help paint the epoxy into corners, I like to cut my chip brush into a wedge shape for the first coat. The long edge still works to paint wider sections of epoxy material, but the pointed end can get into small crevices easily.

Secondly, I do two coats of epoxy. I find that the first coat doesn't always cover completely and sometimes leaves thin spots. When I do the second coat, I add in just a couple drops of black colorant (So-Strong Black, also from Smooth-on), which makes it very easy to see the difference between coats.

A layer of FreeForm Air epoxy putty in the process of being applied over the Epoxacoat mold shell on the owl mask.

The completed layer of FreeForm Air epoxy putty applied over the Epoxacoat mold shell on the owl mask.

The Epoxacoat makes a great base layer, but it's pretty flimsy on its own, so I use a layer of FreeForm Air (you guessed it, another Smooth-on product!) to shore it up and complete the first part of the exterior mold shell. I've talked about FreeForm Air on the site quite a bit, but it's one of my favorite materials to use. It's an extremely lightweight epoxy putty that comes in two parts with a 1:1 mix ratio. There are other materials you can use to shore up your mold shell, such as Plasti-paste or even fiberglass, but FreeForm is my favorite technique and has worked great for my moldmaking over the years.

The clay mold wall has been partially removed but is still dirty, and notes are carved into the clay that read 'cleanup edge, mark keys, pry points, spray/Vaseline'

I let the first part of the mold shell cure overnight, then remove the clay mold wall to start on the second part. Oh, and if you're at all forgetful - like me! - the clay itself is a great place to keep notes and make sure you don't forget any steps. Just smooth it out when you don't need the notes anymore.

The clay will leave some residue on the first part of the mold wall. I use mineral spirits to soften and remove the excess clay and clean up the mold wall edge. I apply the mineral spirits with a brush (another chip brush, or a stiff paintbrush for smaller areas), leave it for a couple minutes, then use the brush to agitate it until it softens and melts off.

I also spend a little time sanding down the exposed edges of the mold wall before I start on the next part.

A clay wedge has been added to the mold wall to act as a pry point.

Next, I create a wedge-shaped piece of clay to use as a pry point. A pry point is an opening in the mold wall that you can use to pry the mold shell pieces apart. I just use a simple flathead screwdriver as a makeshift pry bar. You'll only really need to pry the mold apart when you're first creating the shell (it'll stick to the clay), and when you first pour in the silicone (which kind of suctions itself to the mold wall). After the mold is complete, the pieces will come apart easily with no prying required.

An X is marked in ink on the completed side of the mold showing the location of one of the mold keys.

I also like to place a mark to indicate where the mold keys are. This way, as I'm working my way around the mold wall when prying it apart, I don't accidentally wedge my screwdriver into a key and chip it off. (And yes, I've done exactly that before - hence this addition to my process!)

Petroleum jelly is being applied as a mold release to the exposed mold wall with a paintbrush.

The second half of the mold shell's Epoxacoat has been applied.

Finally, I apply a coat of petroleum jelly as a mold release wherever the second part of the mold shell will contact the first half, and to the PVC pipe forming my silicone pour spout. (Note I've removed my pry point wedge here, but I will add it back on and also apply petroleum jelly around it before the next step.)

Then, I simply repeat the same process again: Two layers of Epoxacoat, followed by the outer layer of FreeForm Air.

The underside of the piece has been prepared for the mold shell to be applied.

The two halves of the front mold shell will stay together quite nicely until I'm ready to pry them apart, so at this point, I flip the whole thing over, clean up any excess clay from the mold walls, sand down the edges, mark my keys, add pry points, apply mold release, and do the whole thing one more time. The process is still the same, two coats of Epoxacoat and one of FreeForm Air.

The completed mold shell with the pry point wedges removed.

In the end, I've got a completed mold shell. Here, I've cleaned the clay out from the pry points, ready to pry the whole thing apart. And...

The completed mold shell opened up, with the mask placed on the clay from the bottom half of the mold, and clay residue still in the two top halves of the mold.

There we go!

Prying the mold shell apart does take a bit of time, so I've learned to be patient with it. I use the pry points to open it up a little first, then work my way around the mold perimeter with my flathead screwdriver to gently open it up a bit at a time, avoiding the keys as I mentioned before. Eventually, it starts to give more and more until it comes free.

Here, I've removed the mask from its cellophane wrap, because for the next part, I'll be adding the silicone that will need to conform to the mask's details directly. I will clean the clay out of the two front parts of the shell, but leave the clay in the back part, because I know the mask is now positioned exactly where it needs to be within the mold shell.

But more on that in the next blog!

All blogs in this series are linked from the Making a Matrix Mold page.


Categories: Costuming
Tags: converting, Epoxacoat, epoxy, epoxy putty, Free Form AIR, key, matrix mold, mold shell, monster clay, mother mold, oil-based clay, owl, owl mask, pry point, resin, resin mask
Live Date: 6/13/2022 | Last Modified: 6/23/2022