Adjusting Firing Temperatures/Cone

[Dan_W]

Hi everybody, I hope you're all doing well and keeping sane during the lock down. Greetings from London!

I'm trying to understand how to adjust glazes for firing at lower temperatures, spending days going round in baffling circles trying to work out even a rough logic for this.

https://glazy.org/recipes/28423

I'm currently trying to get this glaze, Hopper Reticulated, to be more successful at lower temperatures alongside what I'm trying to do with other glazes during the same firing (when I say more successful I mean to crawl more). My kiln struggles to get past 1140 Celsius and I've lost access to the kiln at work due to everything that's going on. This is the only glaze that has began to crawl when working at this temperature, but it's very slight.

If anyone can help me with some advice, I will love you forever. If you can't, I will still love you anyway. Thanks!

[oldlady]

are you just looking for a glaze recipe that makes a glaze that crawls or are you wedded to this particular one for some reason?

[Dan_W]

Hi @oldlady ! Any glaze that crawls at this temperature would be brilliant, I guess I just got enthusiastic about this one due to it doing something.....

[neilestrick]

With most glazes the simplest way to lower the firing temperature is to add or increase the source of boron in the glaze. In that case of this glaze, Frit 3134. It may only take 2-3% to get the results you want. I'd run a test batch, increasing the 3134 by 2% starting at 2%, so 2, 4, 6 and 8%. Since this is a crawl glaze, I don't really know how it will respond. If you find it melts better but ruins the crawl, then you may need to increase the magnesium carb a bit, too, as that's the main thing causing the crawling.

Your other option is to simply find a cone 6 crawl glaze.

[Dan_W]

Thanks @neilestrick. That's super helpful, I'll do a run with those adjustments.

I've tried quite a few cone 6 crawls, none of them coming close to doing anything at 1140 in my kiln.

[Min]

@Dan_W, instead of trying to bring the firing temp down of that glaze I'ld start with one of your existing glazes and run a simple line test.

Take a 200 grams of dry glaze that melts at what you are firing at, roughly cone 2 it looks like, and add 20 magnesium carb (10%) and mix it up so it's a very thick glaze. Dip or brush glaze on a test tile then add 10 (5%) more magnesium carb and do another test tile. Keep adding 10 grams of magnesium carb until you get up to 60. (30%)

The glaze has to be thick, like Yorkshire pudding batter thick, if you don't see cracks in the glaze as it dries it won't crawl much, if at all in the firing.  

edit: fire test samples on a waster cookie (thin slab) or in a scrap shallow bowl in case of glaze runs or pieces of the crawl glaze flaking off, which they are prone to do.

[blackthorn]

I thought to post something but it looks like Min and Neil nailed what you need.

Anyhow,

https://tinyurl.com/uj9dheo

May be of some use.