Reading a Glaze Recipe: Percentages vs. Batch Weights
Those Percentages in Every Recipe
Open any glaze recipe and you'll see a column of percentages. Most potters copy them into a notebook and move on — which works fine! But once you understand what those numbers are actually telling you, the whole thing clicks into place and you'll never mix up a batch wrong again.
So let's decode them properly.
What the Percentage Column Is Really Saying
In a glaze recipe, the percentages describe the base — the core materials that fuse together into the glassy layer. They always add up to 100. Think of it less like "40% feldspar" meaning 40 grams, and more like a ratio: feldspar makes up 40 parts out of every 100 parts of the base mix.
The magic of this is that the recipe scales to whatever batch size you need. Mixing a small 100g test tile? Use the percentages as grams directly. Mixing a generous 500g batch? Multiply everything by 5. The ratios stay exactly the same, so the glaze comes out identical every time.
Additions Are a Different Beast
Here's where a lot of beginners trip up, and honestly it's a bit of a confusing convention — so don't feel bad if this surprises you.
Many recipes list colorants and opacifiers separately, below the base. These are called additions, and they work differently. Instead of being part of the 100%, they're expressed as a percentage of your total batch weight.
So "2% Cobalt Carbonate" on a 500g batch means: 2% × 500g = 10g of cobalt. You mix all 500g of base materials plus 10g of cobalt. Your total dry weight on the scale is 510g, not 500g.
Why does this matter? Because if you accidentally treated the cobalt as part of the 100% base, you'd use less of it than intended — and your blue would come out weaker than expected. Small difference in practice, but worth doing right.
A Worked Example
Let's walk through a simple cone 6 blue so you can see exactly how this plays out.
| Material | % |
|---|---|
| Custer Feldspar | 45 |
| Silica | 25 |
| Whiting | 20 |
| EPK Kaolin | 10 |
| Total base | 100 |
Additions:
| Material | % of base |
|---|---|
| Cobalt Carbonate | 2 |
For a 1000g batch, here's what you actually weigh out:
- Custer Feldspar: 450g
- Silica: 250g
- Whiting: 200g
- EPK Kaolin: 100g
- Cobalt Carbonate: 20g (2% × 1000g)
Total dry material you'll mix: 1020g. Easy!
Why Recipes Are Written This Way (It's Actually Clever)
Once you see the logic, separating base from additions starts to feel really useful rather than confusing.
The big win is flexibility: you can swap colorants in and out without touching the base at all. Want to try iron oxide instead of cobalt? Just change the addition. Want to test the same base at 1%, 2%, and 4% cobalt to see how the blue deepens? Keep the base identical across three tiles and vary only the addition. Clean, simple, repeatable.
It's also how potters share recipes — the base is the stable foundation, and everyone can personalise their additions on top. Once you start thinking of recipes this way, reading a new one becomes much faster.