What is the purpose of overglaze?

[mrcasey]

I recently found an old abandoned box of standard overglazes in our studio closet.  We only fire to cone 05 and 6 electric.   My understanding is that these overglazes are applied

after the glaze firing and then fired to a very low temperature.  The info on the containers is kind of vague about cone temperature and application.  The digital fire pages says that

some overglazes or onglazes are fluxed with bismuth and will melt at around 1300F!  Maybe I could use them in pit firing?  Can anybody tell me a little more about these "overglazes"

and how/why someone might want to use them.                       

[Babs]

I use on glaze.... Majolica glaze plus onglaze dec. I decorate on unfired glaze surface to cone 5/6.

Low firing ...raku as pit firing unless in a saggar will be a mess imo

[Pres]

On glaze, or in glaze is the process of using underglazes or over glazes on an in-fired glazed surface. All so often, the quality of the in-glaze decoration is dependent on the base glaze which is usually white. If the base glaze has zinc as an opacifier, it will have a tendency to dull some of the colors over top like copper greens and some cobalt blues.  Another problem could be tin used as an opacifier where chromium and tin will together can cause flashing of a red/pink color on other parts of the pot or even other pots in the kiln. That is one of the reason many of us have resorted to using titanium, zircopax  or superpax  or even a combination of zircopax and tin or some other opacifier for the white base. I personally have found that zircopax for me is not a nice white without some softening. 

Over the years, I have found my most exciting attempts at surface have come from a combination of dipping, spraying and brushing. Usually in that order. I also have found that these techniques allow me to create texture and pattern whether spraying through stencils, or spraying from different angles over the stamped or engraved clay surface.

 

best,

Pres

[oldlady]

mrcasey,  have you seen the painted plates and other dinnerware that was done about 1900 by "ladies"?    the beautiful full blown, pastel roses that look like a watercolor painting are the ones that come to mind.   they were done with overglaze.    if you look at amazon books for China painting, you can see some really good info, there is a prediction that it is coming back into fashion.

not being a real "lady" that is all i know.   

[Min]

By overglazes are you referring to little bottles of powders or liquids? Overglazes or china paints can come as a dry powder or already mixed up with a brushing medium. The dry sort need to be mixed with either an oil  or water based brushing medium or just plain water, personal preference. Everything, including the pre glaze fired pots has to be scrupulously clean, wipe down the pot with rubbing alcohol, wear gloves so you don’t leave fingerprints. If you are using metallic overglazes wear a P100 respirator, work in a well ventilated area, outside if you can, and when you are finished lauder your clothes and take a shower. China paints / overglazes fired in the 020 - 018 range, well vented kiln for the metallics especially.

Could you post a picture of what you have and someone might be able to give more detailed help. 

[oldlady]

coincidences happen!   a friend gave me some old magazines and i looked at one this morning.  it was "Clay Times" from sept/oct  2002 and the cover photo was a white porcelain bottle by Sam Scott showing his overglaze technique.  

he is working differently now but if you google his name followed by pottery, some of the older work comes up.  his recipe for the colors he uses are for oxides, not whatever you have found. 

overglaze can be much more than i originally thought.

[Babs]

I was thinking that on glaze and overglaze as synonymous.

Then enamels , lacquer china painting as a third firing process at a much lower teml.

As mim says. More details on product or run a few test tiles may give you an insight into how you can use them or not..

[mrcasey]

This is the material I found.  

[Babs]

1lb is an awful lot if infactt t is an enamel or china paint.

I think you have a colourant to be used on unfired glaze or bisqued unglaze imo but testing would get results.

Bismuth, bit toxic...

[Babs]

Any idea record of what pottery was produced in the studio in the past?

[mrcasey]

I suspect that this stuff was never actually used in our studio.  I further suspect that it was taken from a local community college's larders when their

ceramic art program was shut down.            

[liambesaw]

Bismuth, good for the tummy I say

[neilestrick]

Call Standard and see if they have any info on it.

[Pres]

I remember the packaging, this was probably 15 years ago or more. They did make an overglaze material, and it was fired to a lower temp over a pre-fired glazed piece. SC has gotten out of most of these glaze products preferring to use 3 rd party manufacturers it seems.

 

My humble opinion,

best,

Pres