Roy Ceramics

Hello, I fired a piece with no glaze to see if my marbling technique worked- it really didn't pan out how I planned. not much of a marble effect happened- i think the two clay bodies were to similar. So I decided to hand paint onsome underglaze ( black and white) to create a pattern. Should I fire it again ( a second time) or is there a spray fixative I can use on the underglaze? I like the way it looks at the moment- matte painted underglaze and was wondering if a clear fixative would preserve it as is. Any thoughts on which step to take or suggestions of a fixative? Thank you all