Chrome-tin pink is one of the few glazes where the colour is a genuine chemical compound rather than a dissolved colorant, and that makes it both more stable and more fragile than a normal colour glaze. It is stable because the compound forms the same way every firing; it is fragile because zinc, which is in half the glazes in a studio, converts it to a muddy brown at any level above about half a percent.
H 9 · Ø12 / Ø13 / Ø7 cm
Base
The classic chrome-tin pink at cone 04, built on a high-calcium, zinc-free base. The pink is not a pigment added to the glaze; it is a tin-chrome-calcium compound that forms during firing, which is why the recipe is fussy about what else is present.
| Material | Parts | Share |
|---|---|---|
| Frit 3124 | 35 | 32.9% |
| Custer Feldspar | 20 | 18.8% |
| Whiting (CaCO₃) | 20 | 18.8% |
| EPK Kaolin | 15 | 14.1% |
| Silica (SiO₂) | 10 | 9.4% |
| Tin Oxide (SnO₂) | 6 | 5.6% |
| Chrome Oxide (Cr₂O₃) | 0.4 | 0.4% |
| Total charge | 106.4 |
Fired surface
A clear, bright pink with a glossy surface — not a washed-out salmon but a definite rose. Colour strength depends almost entirely on the tin-to-chrome ratio, and the recipe tolerates less than half a percent of zinc before it turns brown.
The compound and the ratio
Chrome oxide and tin oxide in a calcium-rich glaze react during firing to form a calcium-tin-chrome silicate that is pink. The ratio that produces the strongest colour is about 1 part chrome to 15 parts tin by weight — 0.4 percent chrome with 6 percent tin, as here. Going to 1 to 10 darkens toward maroon; 1 to 25 washes out to a pale pink that is barely distinguishable from white.
Chrome is the variable to adjust, not tin. Tin is expensive and mostly acts as the compound partner; chrome is what controls the colour strength. Adjust in 0.1 percent steps.
Zinc, and how it gets in
Any zinc in the recipe — zinc oxide, or a frit that contains zinc — pulls the chrome into a brown spinel instead of the pink compound. Half a percent is enough to shift the colour; 2 percent makes it a chocolate brown. This is why the recipe specifies Frit 3124, which is zinc-free, and why you should never use a bucket that has held a zinc glaze without washing it out thoroughly.
Contamination is the usual culprit when a batch of chrome-tin pink suddenly fires brown. Check the bucket, the sieve, the mixing paddle and the tongs before changing the recipe.
Firing range and atmosphere
Chrome-tin pink wants oxidation and a narrow temperature range. Above cone 03 the pink begins to weaken, and at cone 2 it is a pale grey-pink; below cone 05 the glaze does not melt properly and looks dry. Cone 04 in oxidation is the sweet spot.
In reduction, chrome and tin both behave differently: the pink can turn green-grey, and the surface may blister. This is not a reduction glaze. If you fire in a shared kiln, ask what the previous load was — a kiln that has just been reduced can leave enough carbon in the atmosphere to spoil the first twenty minutes of the next firing.
Mixing and preventing speckle
Chrome oxide is a very fine, very strong powder that clumps badly. Weigh it to 0.01 g, put it in a cup with a little water and a drop of dish soap, and stir it into a paste before adding it to the bucket. Chrome that goes in as lumps fires as dark speckles in the pink, which is a defect on this glaze even though it would be a feature on others.
Sieve the finished glaze through 100 mesh rather than 80. The finer mesh is what eliminates the last of the chrome specks, and at 0.4 percent chrome there is not much margin for lumps.
Steps
- Wash the bucket, sieve, paddle and tongs thoroughly — any zinc residue will brown the whole batch.
- Weigh the five base materials and the tin oxide, and combine them dry.
- Make a paste of the chrome oxide with water and a drop of dish soap, stirring until there are no lumps.
- Add the base materials and the chrome paste to the water and mix for five minutes.
- Adjust to 1.45 specific gravity and sieve through 100 mesh.
- Dip test tiles for one second and fire one to cone 04 in oxidation.
- Adjust the chrome in 0.1 percent steps to reach the target pink, using a fired reference tile.
- Store the finished glaze in a labelled bucket kept away from any zinc-containing glaze.
Where it goes wrong
- Using the same bucket or tongs as a zinc glaze. The colour goes brown and the cause is invisible in the recipe.
- Weighing chrome by volume. A tenth of a gram changes the colour noticeably.
- Adding chrome dry. It clumps, and the clumps fire as dark specks.
- Firing above cone 03 hoping for a stronger pink. It weakens, it does not strengthen.
| Symptom | Cause |
|---|---|
| Pink came out muddy brown | zinc contamination from a bucket, sieve or tongs; clean everything and re-test. |
| Dark speckles across the pink surface | chrome oxide not dispersed; make a paste before adding it to the bucket. |
| Colour is pale and washed out | the chrome-to-tin ratio is below 1 to 25, or the glaze was applied too thin. |
| Surface blistered and green-grey | fired in reduction; this glaze requires oxidation at cone 04. |
Recipe and schedule numbers here were recorded on the workshop’s own kiln. A different kiln, a different thermocouple position or a different clay batch will move the result, so treat every firing schedule as a starting point and keep your own log beside it.