Crawl and Colour

[Dan_W]

Hi everybody!

I've been experimenting with a few crawl glazes I've found on Glazy, such as:

https://glazy.org/recipes/1903

https://glazy.org/recipes/2953

The crawling works, a little inconsistently, but the problem I'm having is that both of these glazes loose their colour. I've tried adding red, pink, blue and yellow stains and they all end up as a uniform cream. 

Has anybody else been through this already?

[Callie Beller Diesel]

Zinc wlll kill a lot of mason stains, and to one degree, so will magnesium in the case of the pinks and some yellows. You might have better luck using oxides to add colour. 

[Min]

5 hours ago, Dan_W said:

I've tried adding red, pink, blue and yellow stains and they all end up as a uniform cream. 

If the pink and red stains are chrome/tin pink and reds then neither of those crawl glazes would work as these stains need a fair bit of calcium in the glaze to get a good colour response and neither of those glazes have it in sufficient amounts. It is possible to use stains in crawl glazes, look at the reference chart for the stains you are using and see what the glaze recommendations are. Example would be all the chrome green stains don't tolerate zinc in the base glaze. If it was a cobalt blue stain then it should have worked, how much did you add? Here are some stains and colouring oxides added to a magnesium cone 6 crawl from Glazy, you can get an idea of amounts from it.

[Dan_W]

On 6/25/2020 at 4:42 PM, Min said:

If the pink and red stains are chrome/tin pink and reds then neither of those crawl glazes would work as these stains need a fair bit of calcium in the glaze to get a good colour response and neither of those glazes have it in sufficient amounts. It is possible to use stains in crawl glazes, look at the reference chart for the stains you are using and see what the glaze recommendations are. Example would be all the chrome green stains don't tolerate zinc in the base glaze. If it was a cobalt blue stain then it should have worked, how much did you add? Here are some stains and colouring oxides added to a magnesium cone 6 crawl from Glazy, you can get an idea of amounts from it.

Hmmm, I'm baffled. I've tried a lot of percentages of blue, even going for 20% out of desperation for the last failed attempt (the suggestion being 8).

[Min]

@Dan_W, which blue stains?

[Dan_W]

@Min The last one I tried was this:

https://www.scarva.com/en/Scarva-Nano-Colours-NC041-Clear-Sky-Ceramic-Glaze-and-Body-Stain/m-2048.aspx

Although not blue, I've also used the lavender from the same range. Thanks for your help with this.

[Min]

That definitely looks like a zirconium vanadium blue stain. Did the high zinc crawl wash out the colour as well as the high magnesium one? Cobalt blue stains, or even just cobalt, should be more stable but the colour will be more of a lavender blue with a magnesium crawl glaze.

[Dan_W]

@Min Yes, both glazes did the same job at stripping out the colour. I'll be ordering some cobalt this afternoon.  Thanks so much!

[oldlady]

dan,  order cobalt carbonate.   cobalt oxide can leave very tiny deep cobalt specks in the finished glaze.    with ball milling, the oxide can be better behaved.