A glaze hydrometer (thickness tester) measures the specific gravity of a glaze, to help standardize the thickness of a glaze from one batch to the next. If you mix your own glazes from recipes or purchased powder, hydrometers can save a lot of misery from glazes too thick or thin. Cut an eight inch piece of half inch doweling. Using a permanent felt-tip marker, mark the side with a centimeter ruler, one mark around for every centimeter, and number them with 1 at the bottom. Seal with polyurethane or shellac (this is important, to prevent marks from becoming illegible, or water logging to affect accuracy). When dry, add a small screw eye to the bottom center of the dowel (pre-drilling with a small bit will help prevent splitting). Secure fishing weight to screw eye by tying with fish line or wire. Determine the proper weight by testing in bucket of water. The weight should be sufficient to pull nearly all of the stick under plain water. In the more viscous glaze, the hydrometer will then stick up higher. To use the tester, drop it into a bucket of glaze, and note the number on the stick. The thicker the glaze is, the lower the number will be. Test your current working glazes, and make note of the resulting number on your recipe page. Then test each new batch. Reading the tester to the nearest half is generally as accurate as is needed. Wet the hydrometer each time before using. It will slide through the glaze better, and be less likely to have the numbers obscured by the glaze.