Glazing over bisqued underglaze

[Cline Campbell Pottery]

A few years ago I glazed clear over an underglaze pattern I'd painted on to a bisqued porcelain plate.  The glaze was comfortably absorbed into the bare white areas, but barely coated the underglazed areas.  I tried again recently and to avoid the water-repelling tendency of the gums in the commercial underglazes,  I bisqued the decorated piece a second time.   I am having the same problem with the glaze not sticking to the underglazed areas.  The glazes were two different kinds of clear, one a studio made, the other Mayco SD-001.  After the first attempt at glazing, I washed off the clear and tried spraying the piece with spray starch,letting it dry, then glazing,  but it didn't help.  The clay I'm using is Laguna Miller MC 550.  The underglaze is usually Amaco Velvet, but some is Duncan or Speedball.

Any ideas?

Cynthia

[Bill Kielb]

Heavily underglazed areas will fill the pores of your clay so the overglaze will tend to not be absorbed as well in the areas of the heavy underglaze. When I have a highly decorated item, I spray these items and allow the decorated areas to dry before spraying another coat. If sprayed too early, I will not be able to build up a reasonable thickness of overglaze as it will be too wet and just run off.  Very similar to applying two coats of paint to your walls. If you don’t let the first coat dry long enough the second coat will never take. My experience, Patience pays dividends for these pieces and slowly build the overglaze thickness as necessary.

[kswan]

You can also test bisque firing a cone or so lower. The underglaze may not be as sintered and can absorb more glaze. 

[Cline Campbell Pottery]

Thank you for responding so helpfully.

Bill, do you spray the piece as evenly as you can, or do you mask off the bare areas?    Do you ever use a binder like spray starch or hairspray?  Can I dry the first coat of glaze with a hair dryer?   Fortunately, I have access to a spray booth at the University where I take a class.  I do use thick layers of underglaze  because I've experienced colors washing out at  cone 5 and above.  I often use porcelain and I like the  vitrification of the higher temps.

K, thanks.  I'll try bisquing at a lower temp.

thanks,

Cynthia

[Bill Kielb]

16 hours ago, Cline Campbell Pottery said:

Thank you for responding so helpfully.

Bill, do you spray the piece as evenly as you can, or do you mask off the bare areas?    Do you ever use a binder like spray starch or hairspray? 

I spray as evenly as I can and often use the half trigger- pull (air only) on the spray gun to gently dry the underglazed  areas with air. Gently from a distance so as not to push the wet glaze around. When in a hurry I have used the heat gun (gently).  Bisque to 05 has had mixed results for me, the clay still absorbs much quicker than the decorated areas so I just apply evenly as if I was spraying any custom finish, like a car for instance and drying the areas with air or heat as needed before the next coat.

I have sprayed many heavily decorated surfaces and patience and even application has proven the most reliable for me. No binders - just smooth even coats.

Next issue you may encounter is certain colors of underglaze applied heavily can cause some overglazes to bubble in the heaviest areas. Our experimentation revealed an overglaze that melts more completely has cured this issue for us as if the underglaze caused that area to not melt fully or evenly. It sort of looks like the opposite when first encountered as if over melted, so I thought it useful to mention if you run into this issue.

I have sprayed, lots of underglaze art btw, often many layers to get the artists correct shadowing etc….. the piece below is to recreate the look of a gem with correct reflections etc…. It is VERY thick with layers of underglaze to get the look.