Single fire a sculpture?

[Karen Mandeville]

Please let me know if these sounds like a good idea. (1)I made this dragon he's in greenware stage I'm thinking of spraying him with greens & blues. When he gets out of the kiln put the shading & details in. (2) I have trays with flowers & details in underglaze I'm thinking of spraying them with clear glaze for a shine & protection too.
Thank you in advance <3

[George Lewter]

I'm not sure what you gain by spraying (underglaze?) on greenware, rather than waiting until after bisque. You can layer underglazes on bisque with very little bleed through of one color into the next. I would think bisque first, spray base underglaze colors, then hand paint details in underglazes, followed with clear satin or matte glaze for the body, and gloss for eyes, teeth, and claws. Substituting glazes for underglazes in this scenario would be asking for trouble as your details would likely dissolve into the base coat (green and blue) glazes.

Clear glaze over underglazes intensifies color and allows thorough cleaning that is impossible on a grainy underglaze only surface.

[Norm Stuart]

I've found firing under-glazed ware to bisque temperature, before applying cone 6 glazes, reduces the blurring of the under-glaze lines during the cone 6 firing.

Seeing stuff move through our kiln, I've seen the quicker approach of applying under-glaze to greenware often causing cracking in the bisque firing if the under-glaze is applied to dry rather than wet ware. But I've not seen this problem develop when underglaze applied to damp or wet greenware.

George Lewter said:

I'm not sure what you gain by spraying (underglaze?) on greenware, rather than waiting until after bisque. You can layer underglazes on bisque with very little bleed through of one color into the next. I would think bisque first, spray base underglaze colors, then hand paint details in underglazes, followed with clear satin or matte glaze for the body, and gloss for eyes, teeth, and claws. Substituting glazes for underglazes in this scenario would be asking for trouble as your details would likely dissolve into the base coat (green and blue) glazes.

Clear glaze over underglazes intensifies color and allows thorough cleaning that is impossible on a grainy underglaze only surface.

[Karen Mandeville]

I'm sorry, I didn't say that the blues & greens were under glaze. I am trying to do single firering. I guess with somethings it's not workable. Thank you so much:)

[George Lewter]

Raw glazing seems to work best on items with a pretty consistent thickness of around 3/16 inch or more. Thinner pieces (or very thin varying to thicker) tend to crack from uneven expansion as they absorb the water from the glaze. The thinner, more fragile areas get relatively more saturated with water than do the thick areas, expand more, causing stress and cracks. It often happens very quickly after glazing, and is more apt to happen with dipping than when spraying. 

If you spray and brush judiciously. Dry very thoroughly. Pre-heat and do your low end heating ramps slowly your proposed method could very well work just fine. To me, the labor going into sculptural work justifies more conservative firing technique (bisque).