Primo vs. Hi-Fire shelf primer

[smallbitz]

What are the main differences between Primo and Hi-Fire shelf primer? I know that you can fire higher with the hi-fire, but do you have to re-apply it each time -even on molds? Please enlighten me

[Laurie Spray]

On our ceramic molds we just apply one good coat of Bullseye primer and they are good for dozens and dozens of firings. I never redo the kiln wash unless I have somehow scratched the surface of the wash.
I only use primo primer on texture molds and that I sand off and reapply each firing.

others?

[smallbitz]

I've been using Hi-Fire (was given to me) and was a bear to scrape off my kiln shelves when it finally started to chip; but it did stay on for many, many firings. I use it on my molds as well, and it works great. I'm almost out, and have some Primo on hand, and wondered if it worked the same, or if you have to re-apply it after each firing? I use thin fire on shelves, but what about my molds?

[Bert Weiss]

KIln wash is not a cut and dry simple subject. You may speak with 5 people and get 6 different stories.

I will speak from personal experience so nobody can contradict me. I make my own kiln washes. I have different recipes for different applications. Most standard kiln washes I know about are a mixture of alumina hydrate and kaolin. Kaolin is clay with a high alumina content. The clay acts as the binder. So, the more clay you use, the harder the wash. Eventually the clay builds up and chips. After it chips, unless you remove it all, the chip leaves a visible mark. There is some temperature between a standard slump and fuse that changes the kaolin. After this change, it sometimes leaves white scum on the glass. For this reason it is recommended to apply a thin overcoat before another fuse firing.

Primo is different, it is a combo of alumina hydrate and an organic gum binder. The binder burns up, and the alumina is easily removed. If you were to replace the binder, I believe it would be re-usable.

When I went to the pottery supply and bought alumina hydrate, the grade I got was coarser than Bullseye's kiln wash. I did some research and found a really neat product by JM Huber called Alumina tri-hydrate SB432. This is finer than the Bullseye grade. If I am making wash for slumping, I use 50/50 by weight alumina and kaolin. This makes a durable wash. If I am fusing, I use less kaolin, and remove it after each firing. On my shelves, when firing float glass, I only need a single coat of my wash to keep the float from sticking. Fusing glasses require a thicker application.

When I work with fusing glasses, I prefer to fire on fiber board that has been dusted with my alumina. I can use this setup over and over, just fine.

I am not sure what the so called Hi Fire is composed with.

[smallbitz]

Thanks all for your advice. I think I'll probably just buy from my local ceramic shop and start mixing my own. It seems to be the most economical and easiest way to go!

[Mike Griffin]

This is a good comparison. It is a PDF http://goo.gl/xEOqu

[smallbitz]

Wow. That IS a really good comparison. Thanks so much the info, Mike! That certainly is helpful.