It is confusing. I would suggest the following instead. That is when I learned what "glaze" and "kiln" are. or maybe: That is when I learned what "glaze" and "kiln" mean. (If you are talking about learning the definition of the words)

The language is OK. The meaning is perhaps a little confusing? To me - knowing what a glaze and a kiln are, are 'quick' understandings. So 'started to know' seems an odd way to describe that realisation. Certainly knowing how to _use_ them properly can take a lifetime...