Why polyester resin?
I’ve been motivated recently to do some polyester resin casting tutorials. In my opinion, the best place to use polyester casting resin is for a piece where you want to put a high polish on the final casting with a buffing wheel and buffing compound. For this resin bracelet, I’m using a plastic bangle bracelet mold and testing out a silicone ring mold. (I always try out all our resin molds before including them for sale in the Resin Obsession store.) For the inclusions, I’m using dollar store ‘Legos’.
By the way, if you are new to polyester resin casting, please read my post on 5 things you need to know before using polyester casting resin before trying this yourself.
What you do not see in this polyester resin bracelet tutorial is me having to talk my peeps that no true Legos were harmed. Trust me when I say it was harder than the casting.
Measure the mold
When working with polyester resin, you have to begin with the end in mind. For my castings, I measured the depth of the molds to determine the amount of hardener I needed to use. (This is not something you need to do when using epoxy or polyurethane resin to make jewelry.) The plastic mold measures 5/8 inches deep, while the silicone mold measures 3/4 inches deep. According to the manufacturer’s instructions, I must add 5 to 6 drops of catalyst per ounce of resin.
What you don’t see here is that I am casting this resin outside. Casting polyester resin in my studio was not an option this week, and because I hate the smell, it had to go outside. Currently, the temperature outside in Florida is in the mid 90’s with fairly high humidity. The ideal temperature for casting this resin is in the low 70’s. Because the temperature is so warm, I knew I did not need that much hardener, but in the name of resin experiments, I decided to do it anyway.
I would regret that decision sooner rather than later.
Knowing I would not have much time to work once I mixed the resin, I wanted to be certain the block pieces would fit into my mold. This means making sure they stay below the edge of the mold in addition to being able to fit into the curve of the mold. Once I was sure pieces would fit, I prepped both molds with a light mist of Petrolease non silicone mold release.
Place the toy pieces
I used a stir stix to place toy pieces into the mold. What you can’t see here is that my resin started to gel in under four minutes. While the right amount of hardener was added to the resin-based upon my measurements, the outdoor temperature put the resin into overdrive. (The manufacturer instructions state I should have 15 to 20 minutes to work with the resin before it starts to gel.) It was a mad dash to shove pieces into both molds. By the end, I was scooping jelly from my cup.
If you have ever had resin get too hot too quickly, this explains why resin gets hot.
This is my finished bracelet. (Upside was the pour side, which is the side exposed to air during curing.) Overall, I’m surprised by how it turned out. Putting gelled resin in the mold to fill it up had me concerned about demarcation lines. Luckily, that didn’t happen.
Of course that doesn’t mean there aren’t some other problems I feel compelled to point out to you. (like this is police interrogation or something similar)
A few of my toy pieces rose up beyond the edge of the mold. I knew this as I was putting the resin in, but didn’t try taking them out once I realized everything was gelling so fast as that would introduce bubbles.
I know, you must be thinking, ‘Well didn’t you put pieces in the mold before you started this?’ How did this happen? I didn’t anticipate how much the pieces would float in the resin.
There are also sharp edges on this resin bracelet that need sanding. That isn’t necessarily unusual as the resin will rise up along the edge of the mold while curing. Unfortunately, though, I cannot sand the bracelet like I usually do because toy pieces are sticking out of the resin. If you have never done this before, this explains how to sand resin smooth.
I will sand the edges so they aren’t sharp, but the top of the casting won’t be flat. No big deal as the bracelet will be wearable and it is for me anyway.
The only other thing to mention is that the bracelet casting side (side exposed to air) was slightly tacky, but not as tacky as I was expecting. I am hoping it will continue to harden over the next couple of days. Since I can’t sand off that surface, I will need to use a layer of resin gloss sealer spray to get rid of the tackiness.
So how did the ring turn out?
In case you didn’t believe me about the resin getting hotter sooner than expected, this ring serves as proof. The inside of the silicone mold used for this casting is perfectly smooth, which should have transferred to the ring’s surface. Instead, the resin got hot and created a spider web-like cracking to the surface of the resin.
The resin is fully cured and the ring is sturdy. Unfortunately though, coating with a layer of the gloss sealer spray will not get rid of the marks. I could try sanding, but I’m worried I would sand down the toy piece or would need to sand too much off the ring shank to where it would break. If I was serious about trying to salvage this ring, I would recoat it with another layer of resin.
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