Bright underglazes becoming dark

[TotterdownPotterdown 0]

Hi, i had some really nice results from stoneware with bright underglazes and sgraffito which looked really vibrant after the bisque firing. But then after applying a transparent glaze and 2nd firing I was disappointed that the colours have darkened and the piece has lost it's 'fresh' appearance. Is there something I can do to maintain the colours? Thanks 

[liambesaw 1,564]

You can try using a clear glaze with no zinc.  Zinc will mute some colors, especially greens, pinks, purples.  But a lot has to do with how hot it's fired too, some underglazes just don't turn out great above lowfire.  You can try different brands.  I really like amaco velvet underglazes but have some mayco ones that look nice at cone 6 as well.

[Callie Beller Diesel 1,709]

You'll find that some underglazes stay nice and bright at higher temperatures, and some of them change or just burn out. Testing is always critical, no matter the brand of underglaze you're using. 

[Gabby 274]

Like Liam, I use the Amaco Velvet Underglazes. On Amaco's website they have photos of how each glaze looks on white stoneware fired at cone 6 and at cone 10, with and without clear glaze over them.

The only color that went from pleasing to me on bisque firing to disappointing at Cone 6 was the terracotta color.  This was my mistake, though. The color samples told me to expect it to go to a toasty brown.

[neilestrick 3,340]

If you're using a brown stoneware, they underglazes will definitely darken some, and going above low-fire temps will also tend to darken them. Every brand and every color behaves differently, and will be affected by the cover glaze, so testing is required.