CLAY - Shrinking.
Clay – Clay shrinking samples
Clays when fired change color, have different textures and shrink. They shrink during drying, firing, and if fired at a high temperature they shrink more than at a low temperature. Most shrink between 5% and 10% so it is extremely important to test the clay you are going to use for the first time and necessary if working on a project which has an exact size.
a) Roll out four pieces of clay, the same size, about 2mm thick 10cm long and 5cm wide.
b) Scratch a code on their backs so you know which is which, then on the front of each one, indent, lengthwise a line 8cm long.
c) Keep one damp and leave the others until they are dry.
d) Fire two of them at different temperatures, depending on the temperature that the clay can take, red clay at 800º C and 1000º C and refractory at 1000º C and 1280º C.
e) Lay out all four pieces, damp, dry, low and high fired, so the bottom edges are in line. The heights of the indented lines will be different, so the percentage of shrinking at each stage can be measured.
f) Make a photo of them together and next to a ruler. File it with all the information on the clay, make, type, color, shrinkage, etc.