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disappearing mocha

updated thu 22 dec 05

 

Dot Burnworth on tue 20 dec 05


I've been playing with "Mocha" ware--or tobacco juice--or what ever
you call it...
I had great results, it was fun to play with, and it bisqued just
fine, but when I covered it with clear glaze, all the manganese
dioxide colorant disappeared...
Any thoughts?
Dot in CT.

Taylor, in Rockport TX on tue 20 dec 05


Hey Dot,

I could be way wrong here, but I always thought that mocha ware was left
unglazed where it was decorated. It seems to me that the clear glaze
would take up and incorporate the Mn into the melt, dispersing it.

Hope you have more chewing tobacco left!

Taylor, in Rockport TX

On Tue, 20 Dec 2005 08:44:48 -0500, Dot Burnworth
wrote:

>I've been playing with "Mocha" ware--or tobacco juice--or what ever
>you call it...
>I had great results, it was fun to play with, and it bisqued just
>fine, but when I covered it with clear glaze, all the manganese
>dioxide colorant disappeared...
>Any thoughts?
>Dot in CT.

June MacDonald on tue 20 dec 05


--- Dot Burnworth wrote:

> but when I covered it with clear glaze, all
> the manganese
> dioxide colorant disappeared...
> Any thoughts?
> Dot in CT.
> Try using a black stain, or Mason's Florentine Green
stain instead of the manganese. The manganese is
absorbed by your glaze, the stains will not be.

June
>
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2ley on tue 20 dec 05


From: "June MacDonald"
>> but when I covered it with clear glaze, all
>> the manganese
>> dioxide colorant disappeared...
>> Any thoughts?
>> Dot in CT.
>> Try using a black stain, or Mason's Florentine Green
> stain instead of the manganese. The manganese is
> absorbed by your glaze, the stains will not be.

Oddly enough, I had a similar experience with black Iron ox, twice. The
first time I used the stain on a bisqued pot, then put a clear glaze over
it. The oxide seemed to turn into a few smudgy spots, which, although it
wasn't my original design, was OK.

Then I tried putting the stain on greenware and firing it, which looked
really good. I followed that by taking the bisqueware piece and coating it
with a clear glaze, and once more the oxide ended up in a few smudges, which
was not OK.

My final solution, since I was using our school's glaze, was to create a
colored slip using the oxide, and that worked.

Philip Tuley

Earl Brunner on tue 20 dec 05


You can glaze over it, but as Taylor says, usually it is left unglazed. If glazed, then a variety of factors need to be considered. Is the colorant strong enough to show and not disperse in the glaze; different glazes act differently and are sensitive to color in different ways. Manganese MIGHT work with the right clear over it, then too, the thickness of the clear will be a factor. Cobalt is stronger than manganese, but the color is different. Someone suggested commercial stains.
Some glazes will not only disperse the color, but might make it run.
So
Try different coloring agents.
Try different clear glazes.
Try different thickness of glaze.

Earl Brunner e-mail: brunv53@yahoo.com


----- Original Message ----
From: "Taylor, in Rockport TX"
To: CLAYART@LSV.CERAMICS.ORG
Sent: Tuesday, December 20, 2005 7:24:26 AM
Subject: Re: disappearing mocha


Hey Dot,

I could be way wrong here, but I always thought that mocha ware was left
unglazed where it was decorated. It seems to me that the clear glaze
would take up and incorporate the Mn into the melt, dispersing it.

Hope you have more chewing tobacco left!

Taylor, in Rockport TX

On Tue, 20 Dec 2005 08:44:48 -0500, Dot Burnworth
wrote:

>I've been playing with "Mocha" ware--or tobacco juice--or what ever
>you call it...
>I had great results, it was fun to play with, and it bisqued just
>fine, but when I covered it with clear glaze, all the manganese
>dioxide colorant disappeared...
>Any thoughts?
>Dot in CT.

______________________________________________________________________________
Send postings to clayart@lsv.ceramics.org

You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/

Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.

Gayle Bair on wed 21 dec 05


Your glaze might be too thick.
I found that using a thinned down clear glaze (between whole and skim milk
consistency) prevents the problem. Brushing the glaze with a foam brush on
gives a light sheen though I use that technique only on outside of
functional pieces.

Gayle Bair
Bainbridge Island, WA
Tucson, AZ
www.claybair.com
-----Original Message-----
From: 2ley
From: "June MacDonald"
>> but when I covered it with clear glaze, all
>> the manganese
>> dioxide colorant disappeared...
>> Any thoughts?
>> Dot in CT.
>> Try using a black stain, or Mason's Florentine Green
> stain instead of the manganese. The manganese is
> absorbed by your glaze, the stains will not be.

Oddly enough, I had a similar experience with black Iron ox, twice. The
first time I used the stain on a bisqued pot, then put a clear glaze over
it. The oxide seemed to turn into a few smudgy spots, which, although it
wasn't my original design, was OK.

Then I tried putting the stain on greenware and firing it, which looked
really good. I followed that by taking the bisqueware piece and coating it
with a clear glaze, and once more the oxide ended up in a few smudges, which
was not OK.

My final solution, since I was using our school's glaze, was to create a
colored slip using the oxide, and that worked.

Philip Tuley

Ivor and Olive Lewis on wed 21 dec 05


Dear Dot Burnworth,=20

Manganese Dioxide has very weak staining properties. You need several =
percent, between 8 and 10 to get a reasonable colour in a glaze, even =
more to get a good tobacco brown.

So the thin film left on your bisque by mocha decoration may be =
insufficient to do more than give anything better than a weak pale =
yellow. I suggest you increase the concentration of MnO2 in your =
original solution.=20

Best regards,

Ivor Lewis.
Redhill,
South Australia.

Dorie Mickelson on wed 21 dec 05


Hi Dot,

There is a great article written by Sarah Bailey (now Sarah Gelsanliter) in
the May 2003 issue of Ceramics Monthly about the Pottery Shop at Greenfield
Village. I'm pretty sure the article includes the recipe for mocha tea that
was developed by longtime potter Ryan Forrey, which has been used at the
Greenfield Village Pottery Shop successfully for the last ten years or so,
and works beautifully!

I am doing a one year apprenticeship there and have not made any mochaware
yet myself, but I can tell you that the Greenfield Village Pottery Shop
(http://www.hfmgv.org/village/libertycraftworks/pottery/default.asp)
produces about 10,000 pieces of early American redware and salt fired
stoneware each year and has perfected numerous early American mochaware
designs (trees, medallions, cats eye, rope/worm pattern, etc.). For the
mocha trees, they coat the pieces with slip at the leatherhard stage, apply
the mocha tea to the wet slip to produce the dendritic pattern, let the
piece dry to the bone dry stage, bisque it, glaze the piece with a clear
glaze, and fire it again. The mocha trees come out crisp and clear with
beautiful background slip colors and a nice glossy clear glaze finish over
them every time.

I highly recommend you check out the Ceramics Monthly article for more
info...but certainly the mix and percentage of oxides you are using
(manganese or cobalt or iron oxide or some stain or whatever) with the
tobacco juice and vinegar, as well as the temperature you are firing your
work to, the glaze you are using, etc., will all impact the final result.

Best of luck!

Dorie Mickelson in cold and snowy Ann Arbor, Michigan, wishing everyone a
happy and healthy holiday season!

www.FreeSpiritCreations.com

****************************************************************************
****

From: Dot Burnworth

Subject: disappearing mocha

I've been playing with "Mocha" ware--or tobacco juice--or what ever

you call it...I had great results, it was fun to play with, and it bisqued
just

fine, but when I covered it with clear glaze, all the manganese dioxide
colorant disappeared...

Any thoughts?

Candida Thorpe on wed 21 dec 05


Hi Dot,
I just had to try mochaware myself years ago.
What I learned from all my mistakes and tests--
Use lowfire clay.
I tried tobacco and mother apple cider vinegar as base for tea, both work
fine.
Use a mixture of manganese, RIO, and cobalt to get a tea that lives past the
glaze fire.
Use nice thin coat of clear.

Of course your mileage may vary.
Feel free to contact me. Happy Holidays,
Candida in FL