How to understand about the glass particle size test

If you've ever worked in glass manufacturing, you know that everything starts with the batch. And one of the most overlooked quality checks is particle size testing.

I've seen more defects traced back to inconsistent raw material particle sizes than almost anything else. Let me break down what you actually need to know.

1. Two Different Tests, Don't Mix Them Up
When people say "glass particle size testing," they're usually talking about one of two things:

Raw material particle size -the sand, soda ash, and limestone going into the furnace. If these aren't consistent, your melt won't be uniform.

Tempered glass fragmentation -breaking tempered glass on purpose to see if it shatters into little pebble-like pieces (safety requirement).

Two totally different tests. Know which one you're dealing with.

2. Raw Materials: The Sieve Test
For incoming raw materials, the go-to standard in the US is ASTM C429.

How it works: take a sample, run it through a stack of sieves, shake it, and weigh what's left on each one. That gives you the particle size distribution.

What matters:

Too coarse → unmelted grains in the final glass

Too fine → dust everywhere, inconsistent melt

Simple as that.

3. Tempered Glass: The Fragmentation Test
For tempered glass, the question is: does it break safely?

Per ASTM C1048 or EN 12150, you hit the glass with a small hammer (about 75g) and count the fragments in a 50mm x 50mm square.

The rule: fully tempered glass needs at least 40 fragments in that area. Fewer than that means it's not properly tempered.

If you're dealing with safety glazing, this test matters.

4. Laser Diffraction: The Modern Way
Sieve analysis works and it's cheap. But for super-fine powders or faster results, labs use laser diffraction.

Shoot a laser through the sample, measure how the light scatters, and the computer spits out a full particle size distribution in minutes. Instruments like the FRITSCH ANALYSETTE 22 NeXT can measure from 0.01 microns up to 3800 microns.

Upside: fast and automated. Downside: costs more than a stack of sieves.

5. What to Ask Suppliers
If particle size matters for your application, here's what I'd ask:

"What standard are you using?" ASTM C429? JC/T 650? If they can't tell you, that's a red flag.

"Can I see the distribution data?" A single passing percentage doesn't tell you much. The curve tells you everything.