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It seems that I can only get one firing from my shelf primer and I have to apply again. I am not sure what I am doing wrong, but it alwyas sticks to the glass. Should I not be able to get several firing from the primer before I have to scrap all the old off and start again. Any help is appreciated.

I) Fire lower and slower.

2) Put iridescent face down against shelf.

3) Use soft glass, black or clear, against shelf.

4) Apply 10 - 12 coats of kiln wash.

5) If you don't like 1 - 4 learn to enjoy applying kiln wash.

Brock

vanpool wrote:It seems that I can only get one firing from my shelf primer and I have to apply again. I am not sure what I am doing wrong, but it alwyas sticks to the glass. Should I not be able to get several firing from the primer before I have to scrap all the old off and start again. Any help is appreciated.

when firing over 1400 i only reuse a shelf - primed with 6 coats of kilnwash - if i'm slumping, firepolishing or tack fusing and staying under 1300 deg. if i am doing lots of firepolishing, tackfusing, slumping i get several firings out of one shelf - cleaning kiln wash is just a part of playing with glass in a kiln

vanpool wrote:It seems that I can only get one firing from my shelf primer and I have to apply again. I am not sure what I am doing wrong, but it alwyas sticks to the glass. Should I not be able to get several firing from the primer before I have to scrap all the old off and start again. Any help is appreciated.

I do the opposite of Brock. I apply one layer and remove and replace it every time I go above 1400ºF. This way I don't have to deal with the chipped build up thing.

Whatever works for you.

I don't get a chipped build up thing. And we're using different glasses Bert. Brock

Thanks for the replies. The Kiln I use is a HotStart by Skutt, and I have not taken the Kiln to very high temps (never above 1500F), so I am not sure that temps are my problem. When I frist started firing glass (only been doing hot glass since March), the primer was good for several firings, but in the last month I only get one firing. I did something today that I had not done in the past, and I hope this will help. Usually I just scrape off the old primer before I add a new coat. Today, after I scraped off the old primer I used some sandpaper on the shelf to remove ALL the old primer. I mixed the primer with a little less water than normal and have started applying layers. I am letting each layer dry before I apply the next one.. in the past I would apply them as fast as I can. I hope this helps... and again, thanks for the replies.

Brock wrote:I don't get a chipped build up thing. And we're using different glasses Bert. Brock

We seem to go around about this about every other month for the last 3 years LOL. I usually mention the different glasses thing, I work primarily with float. I guess the good part of that is the board keeps getting new people and the issues remain the same.

Like I said, whatever works for you.

My experience that led me to find an alternative was back in the mid 80's when I worked with BE. I think Hotline and BE were the available kiln washes. I probably used both. I would coat the shelf each time I fired which was relatively easy. Eventually it would chip and after that the surface sucked and it was very difficult to remove.

Somebody posted a recipe on rec.crafts.glass which I used and liked and still recommend. 80% alumina hydrate/ 20% kaolin. It is much easier to remove than the commercial washes.

Maybe the commercial washes are new and improved?

Either Hotline or BE primer...regardless of the glass, if you fire to full fuse temps of 1500, you will probably need to reprime every firing at those temps just to be safe.

For a mullite shelf I use a 5:1 water to primer mix and apply 3-4 thin coats in opposing directions and dry in the kiln at 500F. IF I fire at 1450 at the high, and the primer looks good, I might fire on it a few times depending on the project. I find that many opals stick regardless...such as white, yellow, neo lav...For a fiber shelf I sand and reprime every time and I use Thinfire too. Not worth the risk of having my shelf ruined because an opal stuck (and lots do even at low temps).

I think your schedules and how you mix and apply your primer and what glasses you use will end up determining how often you have to remove and reapply.

I find that if I put primer on too thick, or too many coats I get burned and that's how I came to the 5:1 ratio and fewer coats.

You will have to find the magic combinations that work for you and your practices.

i use the alumina hydrate/kaolin mix for all jewelry firings -- it gives a better finish on the bottom. it cleans up very easily & it's inexpensive. i use it 50/50.

however, i don't think it's suitable for projects like pot melts. it's more powdery, and i think that powder would get into the glass as it is pushed across the shelf during the drip/melt process. for pot melts, i think the BE kilnwash is the right choice.

cleaning up shelves doesnt bother me. i've got a kitchen spatula that i've been using for years, and the front edge of it is very sharp from the zillions of shelves i've scraped. either type of wash comes off fast. maybe i'm a weirdo ... i kinda like doing it, and i like prepping a new shelf -- there's some anticipation there.

Where does one locate alumina hydrate and kaolin:?:

mirawoodworth wrote:Where does one locate alumina hydrate and kaolin:?:

Ceramic Supply Houses, possibly paint and bake operations. Brock

hey mira -- i buy the alumina hydrate at a ceramics supply place. you can buy these separately, or you can buy a more expensive variety of kaolin that has the alumina hydrate mixed in. i didn't really like it ... i thought it was a little gritty. the alumina hydrate is very soft and powdery, sort of like pudding mix. when you mix it up with the kaolin and paint it on, let it dry. when dry, just wipe the palm of your hand over it in a circular motion, and you'll get a perfectly smooth surface, no effort. that's what i do with my 50/50 mix of the stuff. the place i buy it bags it up for me in 10# bags of each one. i think i'm paying about $1 a lb., but that might be more expensive than what you'll pay since i'm in hawaii and the freight out here makes everything more pricey. good luck. kitty.

Kitty - That's really interesting - I bought a 1 lb bucket of a commercial kiln wash that's pretty good. Now that you describe it, I bet it's the same (or very similar) recipe. In fact the instruction to sand it in a circular motion with your hand is also the same. Thanks!

vanpool wrote:Thanks for the replies. The Kiln I use is a HotStart by Skutt, and I have not taken the Kiln to very high temps (never above 1500F), so I am not sure that temps are my problem.

btw: you're supposed to condition your skutt the first time by firing it very hot, 1650 or so for a while. you'd get a longer life out of it if you do so.