Iron sulfate is a water soluble iron compound. It comes in green crystals that are easily dissolved in water. When it is dissolved in glaze and then dried, it turns a light yellow. Ferrous sulfate heptahydrate is readily available at gardening or hardware stores as a soil pH modifier.
Iron sulfate is not an attractive soluble source of iron in glazes because of its flocculating properties. Gram for gram, it feels like it has similar strength to magnesium sulfate. 1% can greatly thicken a glaze. 4% turns an otherwise normal glaze into jelly.
| Temperature (C) | Solubility (g/100ml) |
|---|---|
| 25 | 29.51 |
Iron sulfate is highly soluble in water, but I still find it easier to dissolve it in water before adding insoluble glaze ingredients.
Iron sulfate is 30% Fe2O3, with the remainder being sulfur oxide and water, both of which will burn away during firing.
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