Introduction: Mold Making: Glove Molds and Mother Molds

By HAR.MS
About: I'm M@. If you know Prototype This, TechShop, The Best of Instructables, Show Me How, or AVPII: Requiem, you've seen some of my work and the cool stuff I've been involved in. I build and design and make and th…



In this tutorial I'm going to take you through the process of making a mold that easily duplicates parts with complex details. I'm going to teach you some techniques for getting the most out of inexpensive silicone, creating molds from parts you can find at your local hardware store, and making incredibly detailed high fidelity castings.

This tutorial is going to cover my process for making a glove mold with a matching mother mold for my production line of Impala Horn Candles (now available on Etsy). I'm going to be making all my castings in wax although this molding method is perfect for nearly any liquid casting material.

For this tutorial you'll need:
Mold making - Many of these items like the fiberglass resin and chip brushes are available at Home Depot
* Casting Silicone (I used Smooth-On's OOMOO 30)
* Spray Mold Release
* PVA (Ployvinyl Alcohol)
* Chip Brushes
* Clay
* Sculpting Tools
* Sculpting Sponge
* Boards
* Hot Glue
* Rubber Gloves
* Shellac
* Fiberglass Mat
* Shears
* Fiberglass Resin
* Stirring Sticks
* Plastic Cups
* Xacto Knife

Casting - You can find most of these materials at your local craft store
* Wicks
* Translucent Casting Wax
* Wax Tint
* Hot Plate
* Oven Mitts or Welding Gloves
* Pliers
* Tin Can

For other tutorials on making molds and casting check out
* Mold Making: Two Part Silicone Mold
* Rigid Urethane Molds
* Casting Complex Parts

For more details on candle making check out
* Custom Candles
* Teacup Soy Candles
* How To Make Candles

Step 1: Prepare Your Model

Ok, so this step assumes you've already chosen something to mold. What makes a good candidate for glove molding? It's usually something with a fairly simple parting line, something that's not going to rip the mold to shreds when you try to take it out. Molds with lots of complex parts, like for an action figure with a billowing cape and huge headgear, probably aren't going to look spectacular. Things like monster fingernails, breakaway glass bottles, and animal horns work well for this method.

I started by filling my horns with Great Stuff, like you can find at Home Depot, to help me adhere them down to my wooden bases. This isn't a completely necessary step, but it meant I could get a really clean seam around the base. I stuck the horns down to my bases, which had been sprayed with clear varnish, with hot glue. Then I pasted some lengths of bamboo to the backsides of the bases to make a funnel through which I could pour the wax once the molds were finished.

It's pretty wise to give everything a final inspection at this point. I made sure there weren't any cracks in between my horns and their bases by filling in the seam with a little window putty. I also gave them a good cleaning to make sure there wasn't any dirt or fingerprints. Everything that you see on your model will end up in the mold and on the finished parts. A little scrutiny here saves a lot of time later.

Once I was happy with all the details I pasted everything down to a plastic sheet with hot glue and prepped everything for silicone.

Step 2: Silicone Top to Bottom

Glove molding is great for low budget casting because it uses such a small amount of your major expense in mold making: silicone. Still, it takes a good deal of practice, trial, and error to perfect any mold making method. If you've never done a mold before it's best to try some small tests with objects you can find around the house before going whole hog and buying every mold making tool and toy. Also, there's a universe of videos on Youtube that show people going through the process of making good molds. Watch them and try to pick up the way the move, the way they handle materials, and all the little tricks that can mean a big difference to your end result. There's also a minimum cost involved in making something like this. Even though it's not too terribly expensive there aren't many ways to cut corners, here. You get what you pay for most times when it comes to fiberglass resins, silicones, and mold releases. If you care about details and how many copies you can get out of your mold, don't try and skimp on the quality of your materials.

So, to continue with the tutorial, our model is on a sheet of plastic that's going to catch all the drips and spills and such as we paint on our first layer of silicone. I sprayed a coat of release on my horns and donned some latex gloves. I own a pretty professional respirator to keep from inhaling fumes in my shop. If you don't have one make sure your workspace is especially well ventilated before opening up your silicone. It's not enormously toxic, but isn't something you want to be breathing in for hours on end.

I mixed up my silicone in a small cup according to the manufacturer's recommendations and began to paint it on my horns starting from top to bottom. When you do this make sure to go slowly and evenly letting the silicone push out bubbles as it travels down your model. Hunt around your model for any air bubbles that might have been trapped and see to them with your brush. Make sure you get under every overhang and into every crack. This coat is going to contain all of your detail. If it's full of bubbles then every part you cast will have bubbles and imperfections as well.

Step 3: Thicken, Rinse, Repeat

The goal from here on out is to create a large enough thickness of silicone all the way around the model so that when we take the model out our silicone shell won't droop or distort. To help out with all of this I mixed sawdust from my shop with my silicone to thicken it at about a 1:1 ratio. It should end up being about the consistency of frosting. I used this to try and even out the form, smoothing the corners and filling in low spots. This helps keep the mold rigid once everything's said and done.

Step 4: Layer Cake

The silicone I used, the OOMOO 30, takes about an hour to set up. I tried to lay on a layer every hour until I was sure there was at least 3/16" all the way around my model. I also made sure to extend the ring of silicone around the base to at least 2". At that point I left it to cure overnight.

Step 5: Parting Is Such Sweet Sorrow

When the silicone cured fully I cleaned up all the hanging solidified drips with a pair of scissors. I then started drawing in my seams. There are two parting lines to get a handle on. The first is the split point between the two halves of what will be the fiberglass mother mold. The other is the cut along the silicone glove mold that allows you to remove the model and all the subsequent castings. I tend to draw mine perpendicular from one another as a matter of preference. I think it helps the cut seam line up in the mold.

Step 6: Clay Up

The next steps are a little tedious, a little fun, and demand an attention to detail. Here's where you're going to build out the form that your mother mold will take. Glue your models (now covered in a thick skin of silicone) to a board, with another board about 1" away from their very tip. This second board is going to provide a flange so that your finished mold can stand upright when you pour your casting material into it.

I started with aluminum foil balled up and stuffed in around my horns to get close to the centerline I drew on them earlier. I didn't want to use any more clay to build out the form for the mother mold than I had to. I then started laying on water based clay. You can find this in craft and pottery stores as wet clay, ceramic clay, stoneware, and water clay. It's super cheap and easy to sculpt.

After I'd laid out a rough layer of clay I went in with some basic tools and sponges to smooth it out. I then added a few divots to the clay to provide a place where the mold could lock back together. These little bumps form what's called keys and are pretty essential to fiberglass molds.

The final step was to coat everything with a layer of PVA and a quick spray of release.

Step 7: Fiberglass

Fiberglass resin is noxious stuff. If you don't have a decent respirator I'd recommend doing this step outside. I like to lay out most of my fiberglass before mixing any liquid resin. I'm not going to go into a super gigantic amount of detail on this step. If you want a tutorial exclusive to fiberglass you can find dozens on Youtube (like this one) and costume communities like http://405th.com have plenty of resources for the inquisitive first time fiberglasser.

I start by laying out patches of fiberglass mat before even mixing resin. The resin is super sticky and makes the task of tearing or cutting patches of fiberglass super hard. Once you have a decent stack of fiberglass laid out mix up a dixie cup's worth of resin with its catalyst and paint your horns, clay, and boards with a reasonably thick coat. Use a chip brush to stick down bits of fiberglass and push them into your layer of resin. Add more resin until the fiberglass is saturated and staying in place. Once a complete layer of fiberglass is stuck down to your mold you can start in with another. Your goal is to create three to four even, bubble free layers of fiberglass. If a bubble develops that you can't brush out, pick at it with your fingertips until it rises to the surface of the resin.

Once you've achieved three or so coats of fiberglass let everything cure overnight. A heat lamp will speed up the process. Heat will also cure any finicky resin that remains in case you didn't properly mix a batch or it met cure inhibition due to any standing water on your clay layer.

Step 8: Flip and Repeat

Now that the fiberglass is all cured it's time to take off the clay and start on the other side. I made sure to paint an even layer of PVA on the fiberglass and spray on some release so I wouldn't be left with a decorative fiberglass sculpture to show for all my efforts.

Just repeat the process for this other side the same as you did before.

Step 9: Trim, Bolt, Cut, and Cast

The next part is really a series of simple steps. Once everything is cured all I had to do was trim off the stringy fiberglass edges, clean everything up with a little sanding, cut the glove molds along the seam line I drew, and install some nuts and bolts into the fiberglass so I could get it back together precisely.

It's pretty essential to drill and bolt a fiberglass sculpture together before you leave it open for any length of time. Fiberglass has the habit of warping a bit as it ages. Being able to make sure it lines up like you originally made it is essential for continued happy casting.

For my candles I simply lay a piece of wick into the glove mold, bolt the mold over it, melt and tint wax in a tin can over a hot plate, and pour into my silicone form.

Step 10: Groovy

That's it. Cast and play and sculpt and duplicate until your heart fills with boundless joy. Silicone is a self releasing material so can make duplicates without too much fuss with anything from wax to concrete to urethane to plaster. It does love to stick to itself, though. If your'e going to make silicone parts you either need to find a silicone sealant or go with a soft urethane mold.

Now it's your job to go out and create! Make awesome things!

If you want your own Impala Horn Candles you can find them on Etsy.