Tutorial – Hot Glue Casting

So, I’ve gotten a few requests to put together a tutorial on how I do hot glue casting with sculpey, so I took a few photos of the process during my last time using the technique. It’s a simple technique and a less expensive option for casting.

Now, first off, this is a tutorial on using hot glue as the mold material, there’s another cheapo casting trick which uses hot glue as the casting material (ie., what you put into a mold and make your final piece out of), totally different. This tutorial makes a mold from Hot glue, which you then use to cast Sculpey. The important thing to remember here is that this is a soft-to-soft technique, the mold and the material are soft, the sculpey will be removed from the mold before firing, so there is going to be some cleanup to do pre-firing.

Materials List:

  • Hot glue gun
  • Hot glue sticks
  • Liquid Latex (the brushable kind, not foam latex)
  • A prototype piece
  • Sculpey
  • Water

Now, to start, you need something you want to make copies out of in Sculpey. This technique is best for one sided/flat backed pieces. In this series of photos, I’m making a mold in order to make a part for a set of matching earrings. First, we find or make the prototype. In this case I sculpted the prototype in sculpey, being sure to get it as smooth and clean as possible, get the flaws fixed now so they won’t show in the replication.

The piece was then fired, smoothed and made as perfect as possible. Now it’s -very- helpful to make sure your piece is secured to the mold prep surface (I like Tinfoil), you want it to be solidly anchored and not have any air or gaps around the edges where it meets the surface.  Then, I brushed liquid latex in a thin layer over the entire piece, being sure to cover it entirely and some of the foil on the edges. Let this dry until transparent.

The latex is a very handy moldmaking tool, it prevents the hot glue from bonding to the sculpey while still retaining most details. Once it’s dry, it’s time to get that glue gun nice and hot, and depending on the size of the piece, you may want to have extra glue sticks ready or even a second glue gun fired up. Quasi-hot glue will not capture details well, we want to keep the heat up.

When applying the hot glue to the piece, start by encompassing the outer edge, right down next to the foil, use the nozzle of the gun to press the glue in and move air bubbles if needed, bubbles won’t kill the mold so long as they aren’t right next to the prototype, but it’s better to have as few as possible. Then start covering the piece in a tight spiral, making sure to cover it completely. It’s also a good idea to add another layer after the first one has cooled slightly, you don’t want thin areas around the prototype.

Once the glue is completely cooled, just pop the prototype out of there! The latex should make this very easy.

Now, it’s time to cast. Any mold/substrate casting will require some sort of mold release (unless it’s silicone), so you’ll want to coat this hot glue mold with sculpey’s release agent, which is just plain ol’ water. Sculpey is an oil based clay and we all know that oil and water don’t readily hang out. So brush a bit of clean water onto the inside of the mold, then press a wad of unfired sculpey into the mold. To ensure maximum shape transfer, you’ll want to press into the sculpey wad firmly with a small diameter flat tool. I often use the end of one of my shaping tools or the end of my x-acto blade holder (take the blade out before grasping at that end!)

Once its pressed in there nice and firmly and you’ve got the back part smooth, flex the hot glue mold to release the sculpey. This is a tricky process, sometimes a little bend of the mold and the sculpey falls right out, sometimes you have to flex it carefully and try to either get hold of a corner of the sculpey and carefully pull it out. If the hot glue isn’t flexing enough, you can always cut a little slit on one of the side walls with an x-acto or very sharp scissors.

Here it is released from the mold, you might be able to see (bad photo) that there’s a little warping on the raised settings of this piece, just do whatever retouching needs to be done on the piece if it got a little warped from de-molding. Its a fairly simple process usually. Then take the sculpey cast and fire it as usual (make sure to always keep that glue mold away from heat! No leaving it beside the oven while you wait for the firing to finish, you’ll have a useless wad of hot glue if you do)

Voila! Towards the top we have the original piece and two copies below it. One of them does have some unevenness, but that sanded down well with the dremel tool.