Turning Glass Scraps into Frit: Is Thermal Quenching Worth It?

I have a ton of clear glass scraps left over from previous projects. As any glass artist knows, glass is expensive, and I absolutely hate wasting a single piece of it!

As a result, I often re-purpose my off cuts into smaller projects like cast hearts. In the past, I’ve used mosaic glass nippers or manually cut pieces down into smaller, frit-like chunks—but doing that by hand can get tedious fast.

With a new project on the horizon requiring over 100 cast hearts, I decided it was finally time to try a faster technique: thermal quenching.

If you haven’t seen this technique on YouTube (I’ll link a few great videos at the end!), the basic concept is simple:

Using a colander, heat scrap glass in the kiln to around 1000°F–1200°F.
Plunge the hot glass directly into a bucket of cold water.
The thermal shock fractures the glass instantly, making it much easier to break down into frit.

Everyone seems to have their own spin on quenching glass scraps. I’ll admit I was pretty intimidated to try it at first, but it turned out to be surprisingly straightforward! Here are my main takeaways from the experiment:

What I Learned

It’s much less scary than it sounds. High heat and cold water feel like a recipe for disaster, but the process was smooth once I got going.
Get a face shield. Opening a 1000°F kiln up close sends a wall of heat straight to your face. Next time, I’m definitely wearing full face protection.
The metal bucket + colander setup is key. I placed the colander directly inside a metal bucket of cold water. By using a metal bucket, I had no concerns of melting a plastic bucket.
I didn’t stress about washing the glass beforehand. I skipped cleaning my scraps prior to heating. My theory? At 1000°F+, most surface dirt and fingerprints burn right off anyway. We shall see!

The Hard Part: Crushing the Glass

While thermal shock fractures the glass internally, you still have to break it down into usable sizes. I tried several methods to get the medium-to-coarse frit I wanted:

Stomping on it: Stepping on the fractured pieces worked reasonably well, but didn’t yield enough fine pieces.
The Car Technique: I really wanted to sandwich the glass between two sheets of plywood and drive my car over it, but my usually supportive husband quickly nixed that idea! 🚗❌
The Hammer Method (The Winner): I ultimately settled on laying the larger glass pieces flat on a heavy towel on my worktable and tapping them with a ball-peen hammer. This gave me the best control over the final particle size. The key was to not hit the glass too hard to keep the shards from flying everywhere.

(Safety note: Eye protection and a proper dust mask are absolute musts during the crushing phase to protect against glass dust and flying frit!)

Final Verdict: Is It Worth It?

The jury is still out on whether quenching glass scraps is an absolute game-changer, but it did produce a solid yield: a small jar of medium frit and a generous amount of coarse frit. The coarse size worked exceptionally well for my 100 cast hearts!

If you want to see how other glass artists tackle thermal quenching, check out these helpful videos: