Why You Should Mix Resin Slowly (Bubbles & Heat)
Every instinct says stir fast. You want the two parts combined, you're aware the clock is running, so you whip it like cake batter to get it over with. And that instinct is exactly what fills your piece with bubbles and, on bigger batches, can even cook the cup. Slow is not the patient-person's preference here — it's the technically correct way.
Here's what fast stirring actually does, and why the boring slow circles win.
Fast stirring whips in air
Think about what a whisk does to eggs: it folds in air on purpose, to make foam. Stir resin fast and you're doing the same thing by accident — dragging air down into the liquid with every quick pass.
Resin is thick and a bit syrupy, so those bubbles don't all rise out before it starts to thicken and set. They get trapped, and you come back to a piece full of tiny craters or a cloudy fog of micro-bubbles. Most of what people blame on "bad resin" is really just air they stirred in. There's a whole bubble fix here, but the cheapest prevention is in your wrist: slow down.
The motion that works
Slow, deliberate circles, like stirring honey into tea. Keep the stick down in the resin rather than lifting it up through the surface, because lifting drags an air pocket down each time. No whipping, no figure-eights at speed, no folding from the top.
It feels too gentle to be doing anything. It is doing the most important thing. And the trade-off for going slow is that you stir a bit longer to fully combine — three minutes is a fair minimum for a small batch — but slow-and-longer beats fast-and-foamy every single time. While you stir, watch the streaks: when those wavy, oily-looking lines vanish and the cup goes uniformly clear, it's mixed. The full mixing method is here.
And then there's heat
This one surprises people. Fast, vigorous stirring doesn't just add air — it adds energy, and energy is heat. On a small jewelry batch that's negligible. On a larger batch it nudges the reaction along faster, and a faster reaction makes more heat, which makes it faster still.
That feedback loop is exotherm, and pushed too far it smokes, yellows, and cracks the resin (and warps the cup). Vigorous mixing of a big mass is one of the quiet contributors. Slow stirring keeps the reaction calm. If you want the full picture of runaway heat, I wrote about it here.
So slow actually saves time
Here's the part that reframes it. Fast stirring feels faster, but then you spend ten minutes chasing bubbles with a torch, or you scrap the piece and start over. Slow stirring costs you an extra minute up front and saves you the cleanup.
I learned this on an early batch of pendants — stirred quick to "save time," then stood there torching the surface over and over trying to clear a galaxy of bubbles that never fully left. The next batch I stirred like I had all day. Came out clean, no torch marathon. The slow one was done sooner.
It really is one of those craft truths that sounds like a platitude until you've watched it play out: slow is smooth, and smooth is fast.
Browse my handmade silicone molds for a clean pour.
Still getting bubbles even when you slow down? Tell me how you're stirring and pouring and I can usually spot where the air's sneaking in.
— Nikolai