BISQUE (b) Sounding tiles
Tiles: if a tile is visibly cracked break it, holding it with both hands and forcing it downward. You might not be able to see the crack, but even so, if the sound is flat, it is advisable not to use this piece, as it could break from the heat of firing. If you are not sure it is broken, put it at the bottom of the kiln during firing, so that if it breaks there is nothing underneath it can fall on and damage. Use it for a one tile design, the replacement of one tile in a large design is too complicated to risk.
When tiles have been cut to a special size or for a border, I do not test them, as the sound changes and I assume that with the pressure used by the cutting machine, they would have broken if they were cracked.
Sounding Tiles: balance it on top of the fingers of one hand and tap in different places, with the first knuckle of your other hand.
Remember: If the resulting sound has a high tone, this means that the tile is not broken. If the sound is flat, it means that the tile is cracked and should not be used.
The next section; Glaze-base (c) Preparing the glaze-base