Kitty on fri 30 jun 06
I mixed up my first experimental (not one of the school studio recipes)
raku glaze today. The recipe sounded a little odd, but I chalked it up
to my lack of experience/exposure. I weighed everything out, mixed the
dry glaze to distribute everything somewhat evenly, added dry material
to water...the glaze went on thick...and GRAINY. I forgot to seive.
Oops. Pot's already glazed, so I figured I'd check and see what it
might look like, planning on sieving and glazing another afterward.
When the kiln hit roughly (everyone tells me those pyrometers ain't all
that accurate) 1200F, I checked on the glaze. The bubbles!! Guessing
it was the glaze starting to melt and would be smoothing itself out
soon, I kept going until I hit 1250F-1300F. Curious as to whether or
not it smoothed that fast, I lifted the kiln...and snatched that runny
mess right out before I would be forced to grind more than the
cookie-shelf bit I had the pot on! Why not...I need the post-fire
reduction practice! It came out of the trashcan what I'm calling "out
to sea Atlantic" blue: really dark and really bright! Pinholes
everywhere in clusters and a shelf shard that's transcended beyond
grinding's ability. *sigh* The joy of testing.
I went back inside to seive, determined that this was just a really
low-temp melter...and discovered that the 400g batch container was warm
to the touch (5 hours after mixing) and the glaze was like concrete.
If I remember my chemistry right, that means a chemical reaction...what
on earth?!?
Any ideas what happened? Here's the glaze recipe. (from a book, even!)
Hal Riegger's Purple
Borax - 38%
Borix Acid - 62%
Talc - 13%
Flint - 6%
Copper carbonate - 6%
Looking at the other recipes in the book and in the school studio, I got
to thinking: is that boric acid supposed to be gerstley borate?
~(a very confused) Kitty
Kitty on sat 1 jul 06
Hi John!
I had the pot sitting in a shelf shard since it was a test, now I know
why that's done! The shard is completely coated, but the kiln shelf got
spared.
Good to know it's a lower melt than average: everything I've used up to
now is 1500F and up.
Thanks!
~Kitty
John Post wrote:
> Hi Kitty,
> The recipes in Riegger's book tend to melt at at lower temperature
> than most raku glaze recipes.
> Riegger has some recipes that are 50% borax and 50% gerstley borate as
> their base.
> These glazes look nice, but you have to get them out of the kiln
> earlier than many other raku glazes.
> *** The one thing that is important to know about these 50/50 glazes
> from Riegger is that they will melt into your kiln shelves. Sometimes
> to a depth of 1/4 inch. So if you are going to use them, fire the
> pots on a brick or a kiln shelf shard so if there is a mishap, you
> don't ruin a good shelf. I bet the borax in your glaze is the reason
> your shelf is unable to be cleaned up.
>
Kitty on sat 1 jul 06
Hi Frank!
I got the recipe out of the Raku: A Practical Approach 2nd edition.
I'm wondering if I should write them to inform them of a possible misprint?
~Kitty
Frank Colson wrote:
> Kitty- Just where did you get this Riegger formula? This is NOT a
> raku glaze formula! When I had Hal Riegger conduct a raku workshop
> here at the Colson Studio in the early sixties, he introduced this KD
> Purple formula which matures, if you want to call it "mature" at C
> 012. Cone 012 is reached at 1591F. The glaze is used only for
> effect and it ends up looking like a purple soda of the '40's., which
> is what it IS to look like. The bubbling will never "de-bubble"
> because it is meant to look like and stay looking like purple bubbling.
> I personally use this glaze rarely, since it is a pain to handle even
> after you put your pot on the fireplace mantle. You'll fined little
> purple bubble shards if you handle it too much.
>
| |
|
