A glaze is a thin layer of glass fused onto a ceramic body in the kiln. An engobe is a layer between the body and the glaze, made with more clay, that hides the body colour and helps the glaze bond and fit.
On a typical glazed tile, the order from the bottom up is body, engobe, printed design and glaze. Each layer is sprayed or poured on before firing.
What a glaze does
The glaze gives a tile or WC its finish. It decides gloss, colour and feel, and it protects the body from stains, water and wear.
Glazes are made by milling frit with clays, minerals, opacifiers and colours in water. The result is a slurry, applied to the unfired body. In the kiln the glaze melts and forms a smooth glass layer.
- Glossy glazes melt fully and give a mirror-like surface.
- Matt and satin glazes contain materials that form tiny crystals or scatter light, giving low gloss.
- Transparent glazes let a printed design show through, as on most digital tiles.
- Opaque white glazes cover the body completely, as on sanitaryware and plain wall tiles.
What an engobe does
Tile bodies are rarely pure white. An engobe gives a clean, even base so the printed design looks right. It also acts as a bridge: it is designed to fit both the body and the glaze, which reduces defects where they meet.
Engobes are made from clays, frit and minerals such as zircon for whiteness. Clay roof tiles sometimes get a coloured engobe instead of a glaze, to give a uniform colour without a glassy surface.
Why fit matters
The glaze and body must shrink by similar amounts as they cool. Glazes are usually designed to contract slightly less than the body. If the glaze contracts more, it ends up in tension and can craze, which shows as a network of fine cracks.
That is why a glaze that works in one factory can fail in another. For the defect itself, see crazing in wall tiles and crazing and pinholes in sanitaryware glaze.
Buying glazes and engobes
Factories either make their own glazes from frit and minerals, or buy ready-made glazes from glaze companies. Ready glazes may come as dry powder to be mixed with water, or as a ready slurry.
If you import glazes or engobes for a factory in your country, the same rule applies as for frit: sample first, trial in the end user's own line, then order. Ask for a technical data sheet, a safety data sheet and the recommended firing range.
For customs, prepared glazes and engobes are usually classified under HS heading 3207, with frit. Confirm the full code with your broker. For the base material, see what types of frit are made in Morbi.
Next step
We can find glaze and frit makers around Morbi, check their production and have samples tested before you buy. To start, book a free sourcing review.