May Luk on sun 8 jun 08
Hello all;
My understanding of an engobe is a slip that can be applied to both cheese-=
hard and bisqued ware. I make my color slip by using left-over B-mix scrap.=
(aka upcycle!) If I want to paint this slip onto bisqued ware, how to go a=
bout? I want to make sure the slip colors matches my engobe color on the fi=
nished products. Calcining my scraps and grind it up is not what I can do. =
=20
Thanks
May
Kings County NY=0A=0A=0A _____________________________________________=
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May Luk on sun 8 jun 08
Hello Bill and friends;
Understood!=20
If I have 100% Bmix - from reclaim - plus water and no additional flux mate=
rials in my slip. How do I find out what is burnt out in my bisque so that =
I can match my engobe slip to the body? A shrinkage test?=20
What I am trying to do is to use up all my scraps, and not to use any new m=
aterials to concoct a recipe. I hope so anyways.
Just thinking out loud.
Thanks again
May
Please reduce, reuse and recycle
>>>>>>>>>>>>
"May Luk"
> wrote:
>=20
> > My understanding of an engobe is a slip that can be
> applied to both
> > cheese-hard and bisqued ware.=20
>>>>>>>>>>>>
> A quick search using key words: "engobe to
> bisque" resulted in the
> following:
>=20
> http://www.duncanshearer.co.nz/glaze/engobes.html
>=20
> http://www.ceramicstoday.com/articles/engobes1.htm
>=20
> http://www.snodger.com.au/tessbrady/ashglaze1.htm#slips
>=20
> So May, best advise: test, test, test!
>=20
> Bill
[...]=0A=0A=0A _______________________________________________________=
___=0ASent from Yahoo! Mail.=0AA Smarter Email http://uk.docs.yahoo.com/now=
youcan.html
Vince Pitelka on sun 8 jun 08
May Luk wrote:
"If I have 100% Bmix - from reclaim - plus water and no additional flux =
materials in my slip. How do I find out what is burnt out in my bisque =
so that I can match my engobe slip to the body? A shrinkage test?=20
What I am trying to do is to use up all my scraps, and not to use any =
new materials to concoct a recipe. I hope so anyways."
May -=20
I like to add several things to an ordinary slip to make it an engobe. =
The primary quality an engobe must have in order to be applied to =
bone-dry or bisque-fired clay is reduced drying shrinkage and early =
adhesion during firing. It doesn't have as much to do with "what is =
burnt out" in the bisque. I add calcined kaolin to reduce the =
shrinkage, and I add 5% Ferro 3134 frit to aid in early adhesion, which =
decreases the chance of the engobe flaking as the claybody and engobe =
shrink separately during the early stages of the firing. There is not =
as much of a mechanical bond as exists with a slip applied to wet ware, =
so that addition of an active calcium-borate frit helps.
Normally, when we know what recipe we are using, we would mix an engobe =
with raw materials, and you would subtract regular kaolin as you add =
calcined kaolin. We don't know exactly what is in B-Mix, but it doesn't =
really matter very much. I would try several versions and test them. =
You will have to add quite a bit of calcined kaolin to make a =
substantial difference. Divide some of the dry B-Mix scraps into small =
test batches, and add 5% 3134 to each of them, and then add calcined =
kaolin in graduated amounts - say 20%, 25%, and 30%, and see how that =
works. If these engobes are going to be used on utilitarian ware, you =
should add a little potash feldspar to aid in high-temperature =
vitrification. The amount of feldspar would depend on the amount of =
calcined kaolin added, since it will make the engobe more refractory. I =
would imagine that B-Mix probably has at least 20% feldspar in it, so =
you could safely add a 20% equivalent of the calcined kaolin addition in =
feldspar. Does that make sense? For example, for the first sample, if =
you had a 500 gram dry sample of B-Mix, you would add 25 grams (5%) of =
3134 frit, 100 grams (20%) calcined kaolin, and 20 grams of potash =
feldspar (20% of 100 grams). =20
In the old standby, "Clay and Glazes for the Potter," Daniel Rhodes has =
a pretty nice chart giving slip/engobe recipes for different application =
stages and firing temperatures. It won't help much in this case, since =
we don't know the base formula of your claybody, but at least it gives a =
good sense of the variations in formula for different slips and engobes. =
=20
As you know, there is still a lot of confusion over the use of those two =
words - slip and engobe. I agree with your usage. I have always =
considered an engobe a slip formulated to adhere and fire on bone dry or =
bisque-fired ware.
- Vince
Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka@dtccom.net; wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka
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