Digitalfire Test Procedure Database

Glaze Hardness - GLHD

Notes

If glazes are underfired or have an unbalanced formula (i.e. lack silica:alumina) they can be soft enough to 'cutlery mark', that is, scratchor mark by metal instruments.

Glaze Hardness Testing Procedure

Method 1: Using a sharp-pointed concrete nail or dry-wall screw, attempt to scratch the surface of the glaze in question. Also watch for any tendency of the glaze to chip, for small holes to develop as a result of under-the-surface bubbles, and for any black marks that show up. Compare its response with that of a glaze known to be good.

Method 2: Using a standard sharp hack-saw blade attempt to 'saw' an area of the glaze surface. Watch for scratches that develop and for black marking. Compare the glaze's response with that of a glaze know to be hard.

If marks, pits, or scratches are left by either method, attempt to clean the surface. If it cannot be cleaned, reject the glaze for food or drink surfaces
.

Variables

VAL - Value (V)

Out Bound Links

• (Typecodes) 5: GLT - Glaze Tests

In Bound Links

• (Tests - Related test) GLFL - Glaze Melt Flow