Underglaze & Glaze discolouring

[bycaitnz]

Hello there, would really appreciate any help I can get!

I have recently switched underglaze to the amaco velvet range due to their colour choice. I have also switched clear glazes but I think the new clear glaze (Cesco super gloss clear) is ruining the amaco colours when fired. My lovely dark olive green now looks like yellow / brown!! Is this because of the clear glaze? Or because of the firing? 

should I stick to the mayco clear glaze? Or maybe Amaco?

See attached an example of the cesco clear glaze vs. the mayco clear glaze

Please help!! i am meant to be launching products in 2 weeks time!

 

[Bill Kielb]

Underglazes traditionally need to be color tested with their proposed overglaze. If you read the underglaze literature, many will speak about color change at temperature and a common issue: overglazes that contain zinc can affect certain underglazes dramatically. Hence for clears, you will often see “zinc free” clear. 

The suggestion is always read the literature, which includes the bottle label, sometimes easier to find on the label than the marketing materials, and always test. Many artists prepare a color palette of all their underglazes with one and two coats of overglaze fired to their typical cone to know the color shift in advance.

[Hulk]

Underglaze colours can be influenced by the clay as well.

[neilestrick]

I have had lots of Amaco velvets color shift on me, especially the greens, even with glazes that should be just fine on them (no zinc). I have much better luck with Speedball underglazes. Looks like the Mayco is the way to go.