 Generally when people discuss the merits of a glaze, they are referring to how it looks when it comes out of the kiln. Now obviously aesthetics reign supreme for artists, but there can be a lot of underlying headaches we put up with when working with a glaze that isn't user friendly. If you have been in the field for awhile, you have likely come across a recipe that settles like a rock in the bottom of the bucket; or a glaze that completely saturates your pottery with water, leaving it soaking wet for hours before you can handle it. Some glazes look great if you apply it just right and it goes into that one special spot in the kiln, but if you forgot to pay sacrifice to the kiln gods your pot will come out looking sad sad sad. The worst is a glaze that has materials that are no longer available. Just in the past two years alone, the Potash Custer Feldspar mine closed, EP Kaolin drastically reduced their output under new management, all North American Talc mines privatized or shut down and Lithium prices have gone sky high with demands from the EV market. Those ingredients have been staples to clay and glaze development over the past 100 years; and as a result of their closures, clay and glaze recipes are all having to adapt and change. These user specific challenges aren't often talked about as 'glaze defects', but in so doing, you can solve for them without losing the aesthetic end result. The method I use to analyze a glaze is to think of it the same way I look at the different stages of greenware in a clay body (ie: slip, wet clay, leather hard, chocolate bar, bone dry). You want to solve for glaze user defects in order of when they appear, working your way towards an end result that looks great and is easy to use. I have broken down the life stages of a glaze into five categories:
If your first reaction to reading this article is "oh crap! I don't know anything about glaze chemistry!", don't worry. Most of the answers come down to being a keen observer and taking notes. (I feel like those qualities could be used to describe many fields of science). Most defects can be solved by adjusting a Hygiene or Process related issues, whether that is dust or oils on your bisque-ware, contamination in one of the materials, or not measuring, mixing, or sieving the materials properly. Changing the chemistry of your recipe should be the last resort to solving any defect. I have created a list of questions below to help you identify the qualities of your glaze. Each question is organized to walk you through the life stages. Stop once you identify an issue in the questionnaire and solve for it before moving on down the list. To learn about each material in your glaze recipe I recommend reading the articles on digitalfire.com/material. If you have any questions about this article, send me a message and I will get back to you. 
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