Ron Roy on sat 15 may 04
and firing
Hi Paul,
First of all - deflocced glaze settles - flocced glazes does not.
Colourants do not deflocc glazes - usually - certainly not ours. I don't
think anyone has complained about that so far.
I'm thinking that your glazes are just too thin - take some of the water
off - enough so that when you dip a dry finger in - you can just see some
skin through the glaze around your fingernails.
It true that some clays hold glaze on better than others. When glazes dry
they usually crack at least a little - when drying and sintering during the
beginning of the firing. If the cracking is not too much the glaze heals
over during the melting. Some glazes are just stiff and they have the most
problem getting back together during the melting stage.
Better to have your glazes well dried before firing for those that tend to
crawl.
If you can be more specific about which glazes are being a problem I may be
able to be more specific.
Impurities in a clay body - that is not bisqued in a way to get the
impurities out does not usually result in crawling but in blistering and
pin holing.
Once firing at cone 6 can be problematic. Many cone 6 glaze rely on boron
to melt. The problem is - if the boron seals over the clay before the
impurities get out - pinholing and blistering can be a problem. Perhaps you
should ask on clay art again - does anyone once fire at cone 6 - and what
glazes work best.
My approach to developing new glazes is to use calculation software so I
can get a handle on expansion and durability - then do line blends.
Let me know if you need more on this - glad to help - RR
>I mixed up a few variations of a glaze from MC6G (the glossy base 2) and
>noticed that without colorants this glaze cakes at the bottom of the
>bucket quickly. I am surmising that the reason for this is that the
>oxides in the other buckets (at 5%) are acting as a deflocculant. Is
>this correct?
>
>In my most recent glaze firing I put in 2 pots that were not bisqued.
>One came out perfect with no flaws at all, the other crawled a bit. The
>one that crawled was a dark red clay and the perfect one was white. Is
>the reason for the crawl due to impurities in the darker body? The same
>glaze on the same clay when bisqued, was fine.
>
>In regards to single firing, What should I be aware of if I opt to do
>this all of the time? It is an appealing idea to me since I could save a
>lot of time and energy if I stopped bisquing altogether. I have been
>bisquing to cone 06. If I continue to bisque what if I drop the firing
>down to cone 012 or 010? What are the implications?
>
>And lastly, How do you develop your glazes? My goal is to have about 6
>glazes that I really like and that are my own creations. I once worked
>with a potter in Santa Cruz who was staring from scratch in his glaze
>development. He settled on a base glaze and then mixed tiny amounts and
>set up a grid on a tile with increasing amounts and different kinds of
>add's. We probably had a few hundred glazes with which to begin further
>tests. Of these hundreds we chose about 20 to test further and then from
>those narrowed it down to 5 or 6. He ended up with some stunning glazes.
>Essentially what we had were variation on the same glaze. That is to say
>one base with different add's. I think that I will follow this route as
>well since it is familiar to me. I am, however, interested in other
>theories on this topic. Any ideas?
>
>I hope everyone has enjoyed spring. Tennessee had been beautiful and is
>only now starting to warm up to those muggy summer days.
>
>Thanks,
>
>Paul Raymond
>Franklin, TN
>
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Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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