search  current discussion  categories  techniques - misc 

mochaware recipe for earthenware-long

updated mon 31 jan 05

 

Trish Messenger on sun 30 jan 05


Hello Everyone,
I have been talking with Kate Johnson off list and I
have shared with her some of my experiences and
frustrations regarding Mocha Tea. I hope that by
sharing what I have learned can save others a
tremendous amount of time.
The Recipe from The Potter's Manual by Kenneth
Clark.

25 grams of finely cut tobacco
1 pint of water
30 grams of iron or manganese oxide

Bring water and tobacco to a boil and let simmer for
20-30 minutes. This is stinky. Sieve through a
kitchen sieve or finer if you prefer. Add oxide and
let it cure for 1 day at room temp. Store in a lidded
(glass) container. No need to refridgerate.

Tobacco can be purchased in pouch or can form at a
tobacconist shop or local drug store. I find that my
cobalt and iron mocha tea improves with age (stored at
room temps) and it smells less pungent.
I have had them for 1 1/2 years and they work
wonderfully.

Mix up slip, Kenneth Clark recommends 3 parts ball
clay to one part china clay. I simply sieved my cone
06-02 white earthenware claybody which I use for my
mochaware (no shrinkage problems here). I do not use
red earthenware with a white slip, only white on
white. One has to work fast with the tea. When the
pot is in between wet and leatherhard stage I dunk the
pot, mix up the tea (oxides settle) with an old
chinese brush and gently touch the surface. With
practice one will learn how to control the flow and
how much tea is necessary. I find that a heavy
concentration will provide the best results under a
clear glaze. After the pot is completely bone dry I
add in other details like tree trunks and mountains
using the mocha tea oxide.

Be careful not to disturb the decoration while loading
the kiln, it is fairly duarable though. Bisque fire
to cone 04. Do not stack pots or tiles on top of the
mocha decoration, It will obscure in the firing. No,
you can not single fire with mocha tea.

Glazing- this is where I have had my problems. My
cone 06 clear glaze would not adhear well on top of
the mocha ware after firing. I experienced glaze
blisters where there were heavy concentrations of
cobalt to having no branches at all with my iron mocha
tea. A recent test I did with Duncan's cone 06, GL
612 clear glaze worked. I did not have any blisters
and my branches were crystal clear. I applied 2 thin
coats with a brush, one vertical and one horizontal.
Kate forwarns that this glaze does get cloudy if it is
applied too thick. However, I may need to add more
than 30 grams of iron to my mocha tea so that it is
more pronounced.
So, after 1 1/2 years of fiddling and making trips
to the shard pile this is basically what I have
learned. I hope that others who are intersted in this
process can find the desired results much faster than
I did.
Best of luck,
Trish Messenger





__________________________________
Do you Yahoo!?
Yahoo! Mail - Find what you need with new enhanced search.
http://info.mail.yahoo.com/mail_250

Kate Johnson on sun 30 jan 05


Hello Trish and all who have been discussing mochaware, both on and
offlist...

> Hello Everyone,
> I have been talking with Kate Johnson off list and I
> have shared with her some of my experiences and
> frustrations regarding Mocha Tea. I hope that by
> sharing what I have learned can save others a
> tremendous amount of time.

Thank you for sharing--

One thing I mentioned the other day was that for me, the cobalt oxide mocha
tea held its definition better than manganese dioxide and MUCH better than
iron oxide. The RIO worked well when it was very very fresh, but after a
few days, even with stirring and re-seiving, after a few days it lost most
of its power to branch. I tested it again yesterday, after a few weeks, and
again got almost no result. I don't believe that post went through, but I
thought it might save others some frustration knowing what worked best for
me.

The problem with the branching may be in part the RIO I was using, however.
I have had problems with it in my glazes, as well, and will be testing new
RIO this week. That, to me, is the value of this list, in part. You can
read all the books and recipes in the world--and I certainly have read all I
can get my hands on here--but sometimes it takes an experienced potter to
recognize that perhaps it's your material that's the problem, not you.
(Thank you, Snail!)

>
> Bring water and tobacco to a boil and let simmer for
> 20-30 minutes. This is stinky. Sieve through a
> kitchen sieve or finer if you prefer. Add oxide and
> let it cure for 1 day at room temp. Store in a lidded
> (glass) container. No need to refridgerate.

This is something I found interesting in Trish's experience, the fact that
she does not refrigerate, and that she's been using the same tea for a year
and a half. Most of the recipes I've found suggest throwing the tea out
after a week as it will have lost its ability to branch. Perhaps they were
speaking of RIO and the tendency of iron to clump after a while, because my
manganese and cobalt teas worked as Trish says, very well after aging 3
weeks or so, also without refrigeration.

By the way, Bonnie Staffel, Lili Krakowski and I have been discussing this
process, offlist, as well...Bonnie suggests a bit of CMC or other
deflocculant in the slip; Lili was wondering about a bit of gum in the mocha
tea--more experiments follow.
>
>
> Mix up slip, Kenneth Clark recommends 3 parts ball
> clay to one part china clay. I simply sieved my cone
> 06-02 white earthenware claybody which I use for my
> mochaware (no shrinkage problems here).

That's what I use as well, and have no problems with fit between the slip
and the clay body. Unlike Trish, I DO use red earthenware under a white
slip. I've experimented with putting the slip on an almost wet clay,
leather-hard, and even bone dry--all work equally well, the only difference
being when I'm doing sgraffito--very nice crisp lines on the bone dry
surface. The slip does, however, dry more quickly on a dry surface, so may
not be appropriate for mochaware--you want that slip to be WET when you drop
the mocha tea in.

I do not use
> red earthenware with a white slip, only white on
> white. One has to work fast with the tea. When the
> pot is in between wet and leatherhard stage I dunk the
> pot, mix up the tea (oxides settle) with an old
> chinese brush and gently touch the surface. With
> practice one will learn how to control the flow and
> how much tea is necessary. I find that a heavy
> concentration will provide the best results under a
> clear glaze.

As did I. I use a stronger concentration of oxide than the recipes
generally call for. My first attempt, following the recipe exactly,
produced a very weak, pale branching. I more than doubled the amount of
oxide and it worked much better.

I do find that the manganese dioxide resists the clear cone 06 glaze I was
using, where it is strongest, in the center of each branch-form, resulting
in a dull area. This does not happen with the cobalt, FWIW.



>
> Glazing- this is where I have had my problems. My
> cone 06 clear glaze would not adhear well on top of
> the mocha ware after firing. I experienced glaze
> blisters where there were heavy concentrations of
> cobalt to having no branches at all with my iron mocha
> tea. A recent test I did with Duncan's cone 06, GL
> 612 clear glaze worked. I did not have any blisters
> and my branches were crystal clear. I applied 2 thin
> coats with a brush, one vertical and one horizontal.
> Kate forwarns that this glaze does get cloudy if it is
> applied too thick. However, I may need to add more
> than 30 grams of iron to my mocha tea so that it is
> more pronounced.

It may be that the bottle I have is old, though--I don't know if fresh
Duncan GL 612 would do that. More experimentation is in order.

> So, after 1 1/2 years of fiddling and making trips
> to the shard pile this is basically what I have
> learned. I hope that others who are intersted in this
> process can find the desired results much faster than
> I did.

Many thanks, Trish, from all of us...we will continue to report results.
I'm testing a new set of tiles today...

Regards,
Kate Johnson
Graphics/Fine Arts
http://www.cathyjohnson.info/
http://www.epsi.net/graphic/
http://www.ebsqart.com/Artists/cmd_1494_profile.htm