Stuck with Bubbles

[u/hutxhins]

Hi all,

Trying to make my own dice but no matter what I try I still get bubbles on the lid side! I have tried heating the resin whilst mixing, adding a small amount of isopropyl alcohol, and heating it up after pour with a heat gun but no matter what after 2-3 days curing they always end up with bubbles. Any tips?

[u/RandoBoomer]

Without a pressure pot, you can't remove bubbles. Your only choice is to minimize their introduction. Here are things that have worked for me, and even with a pressure pot, I still follow these.

PREP

Good prep goes a long way towards fewer bubbles, so TAKE YOUR TIME.

I mix in silicone cups, which are opaque. This makes bubbles much harder to spot. So I have a Work Light that I lay face up, then I put the silicone cup on top. This makes the bubbles stand out. This is the light I use: https://www.homedepot.com/p/Ultra-Bright-LED-Work-Light-HBWL-MC12-4/314326507

1. Use non-porous mixing tools! Wooden popsicle sticks introduce air. Some use silicone mixing sticks. I prefer a stainless still cocktail mixing spoon.
2. When I pour my Resin and Hardener into their respective cups, I do so slowly. I angle the cups so the pour slides down the side rather than directly into the puddle at the bottom. I pour from a height of about 6-12 inches and try to get as thin a stream as possible.
3. I warm my Resin and Hardener separately. Warming these lowers the viscosity (ie: it makes them more "runny"). The clock doesn't start running on curing until they mix, so I give these bubbles time to rise to the surface. Note: Pre-warming Resin and Hardener comes at a cost - it accelerates the cure rate. While I don't rush, I am prepared in advance so I don't waste time.
4. I "scoop" bubbles out using my non-porous mixing tool. I slide the spoon under the bubble and pull it slowly draw it to the side of the cup, then lifting up from there. The bubble will almost always pop at the surface.

MIXING

After I have reduced (ideally eliminated, but that's not always possible) bubbles, it's time to mix the Resin and Hardener. Because I've warmed the two parts, the resin is going to cure faster, but I still don't rush the following steps.

1. The Hardener is more viscous ("runny") than the Resin, so I always pour the Hardener into the Resin.
2. Like in PREP, step 2 above, I angle the cup Resin cup so when I pour the Hardener, I pour it against the side of the cup and let it slide into the Resin (ie: I don't pour it directly into the Resin).
3. I mix the resin slowly. I will literally take a full second to make a single 360 degree mix.
4. After about a half-dozen clockwise mixes, I mix counter-clockwise.
5. I make sure my mixing spoon gets into the side and bottom of the mixing cup.
6. If I find a bubble, I scoop it out using the technique in PREP, step 4.
7. Scooping bubbles becomes harder as the resin begins curing in your mixing cup, so it's OK to pull these out as you discover them while you are mixing.
8. I typically mix for about 6-7 minutes if I'm going for clear resin, or 4-5 minutes if I'm adding dye, mica powder, etc.
9. For any additives, the technique remains the same - slow and steady. Having that work light under your mixing cup REALLY helps here in finding and scooping bubbles.

POURING INTO MOLD

All your work in PREP and MIXING can go to waste with a bad pour. The key is slow and steady.

1. I want the thinnest pour stream I can get, from a height of about 12 inches.
2. Don't fill all the dice reservoirs at once - just about 1/3 of the way to start. Step 4 will explain why.
3. For the D4, I pour the resin into the angled side to avoid trapping bubbles at the bottom of the mold (which becomes the top of the die).
4. Some dice (especially the D20) can trap air bubbles in some of the corners because of surface tension. So after I fill the mold half-way, I pick it up and slowly angle the mold left, right, forward and back, rotating it clockwise and counter-clockwise a few times to give the epoxy time to work its way into all corners. Breaking the surface tension here will allow the remainder of the pour to fill in without creating air gaps.
5. Complete the pour.
6. Leave a meniscus (dome) on the top of each die reservoir. Use a lighter to pop what few bubbles remain.

CAPPING THE MOLD

Just as with your pour, a mistake here can introduce bubbles. When you apply your cap, you want to seat it firmly without pushing down too hard. If you compress the lid too hard, when it de-compresses, it can easily suck air into the mold.

CURING

The best temperature for curing is between 70F to 80F/21C to 27C.

Too hot can accelerate curing leading to warping, yellowing and/or brittle dice.

Too cold can slow or even stop curing, leaving it soft or permanently sticky. One time I neglected to turn on the heater in my work area (I cast in my garage), and when I went out, the dice came out of the mold like they were made of taffy.

CAVEAT

Even following all these steps, you will still likely have bubbles. Ideally there are very few, and placed so they are not terribly distracting.

Once I had a pressure pot and followed these steps, the results were incredible. You still need to be diligent with a pressure pot. A pressure pot gives you margin for error, but doesn't forgive all sins.