John Hesselberth on wed 29 may 02
on 5/29/02 2:40 PM, Mark A. Dyer at ddmg@ISERV.NET wrote:
> I am
> using Ron and John's formula for base gloss 2 trying to achieve the
> Licorice Black but keep ending up with what looks like the skin of an
> Avocado. It is a great green with breaking browns, but I am so @#%^7
> frustrated trying to get black.
Hi Mark,
I could only guess that you do not really have cobalt carbonate in your bag
labeled as such. Is it lavender powder in the bag? If not that is your
problem. You may also be applying it too thin, but I'm most suspicious of
your cobalt--I suspect it is either not cobalt or it is of very, very low
purity.
Regards,
John
web sites: http://www.masteringglazes.com and http://www.frogpondpottery.com
EMail: john@frogpondpottery.com
"It is, perhaps, still necessary to say that the very best glazes cannot
conceal badly shaped pots..." David Green, Pottery Glazes
Mark A. Dyer on wed 29 may 02
Hi All
I am in need of some Fresh thinking for a problem I am having. I am
using Ron and John's formula for base gloss 2 trying to achieve the
Licorice Black but keep ending up with what looks like the skin of an
Avocado. It is a great green with breaking browns, but I am so @#%^7
frustrated trying to get black.
Ferro Frit 3134 26%
Custer Feldspar 22%
Talc 5%
Whiting 4%
EPK 17%
Silica 26%
Added:
Red Iron Oxide 9%
Cobalt Carbonate 2%
Other test I varied the ROI % up and down, and varied the Cobalt %up
and down . The test tiles were dipped, single brushed and double brushed
I am using a white buff stoneware body, firing to cone 6 with the vent
on, I did shut the vent off and plugged the pep holes at around 2100F.
20 min soak at the end. I'm sure I am over looking the obvious and feel
that it is almost like a reduction firing. Shot of having me committed
any help would be greatly appreciated
Thanks
Mark
Mark A. Dyer
mark@stewartiastudio.com
http://stewartiastudio.com
Paul Taylor on thu 30 may 02
Dear mark
This glaze is a typical iron saturated glaze and depends on the firing
cycle and the atmosphere for the black you are looking for so do the test
again and take ring pulls out as the glaze cools . My bet is that your kiln
is so well insulated that the glaze is cooling down too slowly and so well
air tight you may be getting some reduction but in this case I doubt if
reduction matters.
There is a dynamic between temperature and cooling if you fire higher the
slow cooling may not mater because you decrease the potentiality for
crystallization with a higher firing. but temocue crystallizes too easily
Iron is very susceptible to change in glazes according to temperature and
cooling rates
You could open the kiln up and make sure you cool past the
crystallization point a bit faster 1900F seems to be a magic number if you
want shiny you have to cool quickly well below this temperature but draw
rings will give certainty.
again the usual advise make sure the kiln is turned off, obvious! I know,
but if you are as absent minded as me ---- we hitch the weekly bin to the
car to take it up the drive to the pick up point . I drove it to town the
other day :( .
By the way I am wrong often enough so I would like to know how you get on.
--
Regards from Paul Taylor
'Craftsmanship is art'
http://www.anu.ie/westportpottery
phone 098 21239
Paul Taylor
Westport pottery
Liscarney
Westport
County Mayo
Ireland
> From: "Mark A. Dyer"
> Reply-To: Ceramic Arts Discussion List
> Date: Wed, 29 May 2002 14:40:18 -0400
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Help with black
>
> Hi All
> I am in need of some Fresh thinking for a problem I am having. I am
> using Ron and John's formula for base gloss 2 trying to achieve the
> Licorice Black but keep ending up with what looks like the skin of an
> Avocado. It is a great green with breaking browns, but I am so @#%^7
> frustrated trying to get black.
>
> Ferro Frit 3134 26%
> Custer Feldspar 22%
> Talc 5%
> Whiting 4%
> EPK 17%
> Silica 26%
>
> Added:
> Red Iron Oxide 9%
> Cobalt Carbonate 2%
>
> Other test I varied the ROI % up and down, and varied the Cobalt %up
> and down . The test tiles were dipped, single brushed and double brushed
>
> I am using a white buff stoneware body, firing to cone 6 with the vent
> on, I did shut the vent off and plugged the pep holes at around 2100F.
> 20 min soak at the end. I'm sure I am over looking the obvious and feel
> that it is almost like a reduction firing. Shot of having me committed
> any help would be greatly appreciated
>
> Thanks
> Mark
>
> Mark A. Dyer
> mark@stewartiastudio.com
> http://stewartiastudio.com
>
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