search  current discussion  categories  techniques - slips 

melt point crystalline glaze-decorating slip/engobe

updated mon 16 nov 98


Lawrence Carter on sun 15 nov 98

Hello Craig Martell,
Thank you for your interest in my questions and your reply.
The idea of using 'draw trails' is promising. Perhaps a little
dangerous to use a steel rod to probe into an electrically fired kiln.
The actual spy holes in my kiln are about 35mm in diameter which renders
access difficult yet I still find the idea has merit . Forming a large
spy hole in my electric kiln ,the outside being lined with thin
stainless steel jacket is a little daunting .
I was wondering if it was possible to predict the melt point to within
+- 20 degs C by a calculation method, if so how ?

In message <001f01be0f92$e26eb2e0$1a896ac6@pavilion>, Craig Martell
>----------------------------Original message----------------------------
>Hello Lawrence:
>I remember one of your initial questions about finding the fusion temp of
>your crystalline glaze. One way to approach this is to use draw trials.
>Make some coils and form them into small circles that will sit upright and
>place them in the kiln near a spy so that you can pull them out at different
>temperatures. Just glaze the upper part of the coil because of the runny
>glaze factor. Watch the pyrometer and pull trials at temps where the glaze
>is likely to start fusing. I use draw trials in the salt kiln, and pull
>them out with a thin steel rod. Wear gloves!
>As for the slip-engobe thing, am I correct that you are placing a slip over
>a glaze? If so, the curling that you are getting is normal. Slips will
>almost always have a higher clay content than a glaze and will shrink more.
>This will cause the curling and crawling. You will need to calcine some or
>most of the clay in the slip to get this to work. Multiple application
>methods are tricky and crawling and shelling is a common problem. Try to
>apply one material over another as soon as the initially applied glaze or
>slip loses its sheen but hasn't dried and done all it's shrinking. Timing
>can be a critical factor. Applying raw slip to bisque ware is not usually
>successful unless you've calcined some of the clay in the slip or reduced
>the raw clays considerably. This is a tough one to answer well and I hope
>I've helped a bit.
>regards, Craig Martell in Oregon

Lawrence Carter