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Engobe Questions

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Hey everyone ...

I am doing my thesis and i am doing ceramics first time for my thesis .since i found this site is helpful can you guys solve my problem.

Iam using engobe to color my terracotta ceramic pieces but unfortunately before applying engobe on my final pieces i tested some tile but the results were not very much in my favour i have applied stain color engobe  on my tiles and fired them then i applied clear glaze on them but after second firing my stain color engobe was washed away under from clear glaze and terracotta body original colour is showing now. Can anyone help me to solve my problem. I really need help

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Hi Sahar!

I'm curious to see what responses you get ...meanwhile, please supply more detail, the composition of your engobe, what you are using to colour/stain it, the thickness of application, and when are you applying it (before or after bisque fire). Also specify your clear glaze recipe, firing temperature, and any detail on the clay body you might have.

I'm working in mid range (cone 5/6) stoneware - had some success blending clay with water, sieving out the sand and/or grog, pouring off some water after settling, and using the result on green ware. I particularly like the red and white over contrasting colours. The slip goes on nicely with a brush, however, timing can be a factor, as significant moisture is added to the piece, hence it has to be stiff enough; I'm brushing on after trimming, at the wheel. The coatings are tight after bisque, but not diminished, however, the slip does diminish in the glaze fire; I like the effect.

Here the red slip was brushed on, then dapped with the brush tips whilst the wheel slowly turns - the white(ish) clay was completely covered.

 

srf over speckly white bowl.JPG

Edited by Hulk
missed an en

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It will help to figure this out if you post your engobe recipe, which stains you are using and the percentages of those you are using plus your clear glaze recipe.

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Some colours will "burn" out at certain temps. 

Some glazes will interact with the stain.

The layer of engobe if not thick enough can become more transpatent as the temp rises.

A thesis hey!

Great yime for a miltitude of testings!

 

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It looks like you are using what is basically a low fire claybody recipe. The recipe below was given to me by George Vardy of Mason Stains, might be of use to you. One other thing, the covering glaze has an effect on the stains. If for example you use a stain that has certain requirements for colour stability such as a chrome tin red then the covering glaze must have high calcium. If the stain is a chrome green (most but not all are) then no zinc in the covering glaze. This type of info should be available from your stain manufacturer. There is a lot of debate about the terms engobe, slip and underglaze, to me this falls under the underglaze category as the clay content is fairly low.

Mason underglaze recipe: all temp's (measured in part not by weight)

EPK Kaolin 10 parts

Feldspar.     25 parts (doesn't matter if it's a potash or soda spar)

Flint.            25 parts

Stain.           40 parts

Mix well with water, add 1 part VeeGum T that has been FULLY broken down in water, screen through 100 or finer screen, bring to your painting consistency by addition of more water if needed. (the VeeGum T is necessary for suspension, Bentone Ma (aka macaloid) can be subbed for it)

When using very strong stains such as cobalt blues or chrome greens you may need to reduce the amount of stain if the fired colour is too strong for your requirements. Refractory stains such as the chrome greens might need an addition of another flux such as whiting to increase melt.

edit: any reason you are using boric acid rather than a less soluble form of boron?

 

Edited by Min

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