Mark Mondloch on tue 27 oct 98
Hi,
I was wondering if anyone would like to explain how cobalt produces
green in this glaze instead of blue. I'd like to try is alter it to be a
little more fluid, but don't know how to change the recipe without
losing the green. Any comments on it's safety/durability?
Reitz Green Matt:
70 Neph Sy
5 Whiting
2 Gerstley Borate
15 Petalite
8 Ball Clay
Add:
1 Cobalt Carb
1 Rutile
Thanks,
Sylvia Mondloch
--
Mark & Sylvia Mondloch
Silver Creek Pottery & Forge
W6725 Hwy 144
Random Lake, WI 53075
mondfam@execpc.com
http://www.execpc.com/~mondfam
Alexander Solla on wed 28 oct 98
Sylvia-
Green from cobalt is actually intimately related to the use of rutile
in this glaze.
If you want to keep the green but want it to be more fluid try increasing the
whiting content a bit or decreasing the ball clay a bit.
You could also play around with different bases and keep the colorants the same
ie. find your favorite glaze and try the cobalt and rutile combo and see
what you think of that color.
I will caution though, that part of the reaction is also caused by
the lithium in the petalite... that in combination with the cobalt and ti and
iron all add up. So, play with it, test it and try something else.
ALex Solla
Craig Martell on wed 28 oct 98
>----------------------------Original message----------------------------
>Hi,
>I was wondering if anyone would like to explain how cobalt produces
>green in this glaze instead of blue. I'd like to try is alter it to be a
>little more fluid, but don't know how to change the recipe without
>losing the green. Any comments on it's safety/durability?
Hello:
The rutile which contributes some titanium is influencing the green. This
usually requires more than 1% rutile but this base seems to be real
receptive to titania influence. High sodium glazes help develop this green
and Reitz Green is very high in sodium.
It's a durable glaze with plenty of alumina and silica but the high sodium
content from the Neph Sy makes this a real crazer and it will leach cobalt.
How much cobalt? I don't know, and you'll have to test it to find out.
I've used this glaze on several test pieces and have seen it craze on a
balanced cone 10 porcelain. It's a beautiful dark green matt. Lovely
surface and does outrageous stuff with colored porcelain slips.
The receipe I have uses EPK instead of Ball Clay so it's a bit more
refractory than the receipe that you are using. You might try replacing
all, or some of the Petalite with Spodumene to raise the level of lithium
and produce a stronger melt. You could also raise the Gerstley Borate a bit
instead of messing with the Petalite. When you get what you want,
recalculate the glaze to determine the balance of the glass. Petalite is
contributing the lions share of silica to this glaze and that's something to
be aware of.
regards, Craig Martell-Oregon
David Hewitt on thu 29 oct 98
Mark,
Rutile contains titanium and this can give green with cobalt.
If you would wish, I can send you a jpeg picture of a set of test tiles
showing the results of a triaxial blend of a glaze with cobalt oxide and
titanium oxide up to 10% and tin oxide up to 5%. The addition of
tianium oxide produces greens and tin oxide blues. The tests were done
to illustrate he effect of opacifiers on a cone 8 glaze with different
colouring oxides. If you would like to see this please email me.
David
In message , Mark Mondloch writes
>----------------------------Original message----------------------------
>Hi,
>I was wondering if anyone would like to explain how cobalt produces
>green in this glaze instead of blue. I'd like to try is alter it to be a
>little more fluid, but don't know how to change the recipe without
>losing the green. Any comments on it's safety/durability?
>Reitz Green Matt:
>70 Neph Sy
> 5 Whiting
> 2 Gerstley Borate
>15 Petalite
> 8 Ball Clay
>Add:
> 1 Cobalt Carb
> 1 Rutile
>
>Thanks,
>Sylvia Mondloch
>
>--
>Mark & Sylvia Mondloch
>Silver Creek Pottery & Forge
>W6725 Hwy 144
>Random Lake, WI 53075
>
>mondfam@execpc.com
>http://www.execpc.com/~mondfam
>
--
David Hewitt
David Hewitt Pottery ,
7 Fairfield Road, Caerleon, Newport,
South Wales, NP6 1DQ, UK. Tel:- +44 (0) 1633 420647
FAX:- +44 (0) 870 1617274
Own Web site http://www.dhpot.demon.co.uk
IMC Web site http://digitalfire.com/education/people/hewitt.htm
Tom Buck on thu 29 oct 98
Sylvia M:
If you are able, find a book discussing properties of sunlight.
"White" light is a blend of the spectrum, from invisible infrared to
invisible ultra-violet, in between are all the colours our eyes detect.
The colour spectrum can be defined in terms of wave-length. The equation
describing the relationship is V = f.n (velocity of propagation equals the
frequency times the wave-length).
The wave length of green light is slightly larger than the wave
length of blue light, so if the reflected light from the pot is shifted
slightly one gets green rather than blue. If the glaze is made less acidic
(less alumino-silicate, more alkali & alkaline earth oxides) its fine
structure is altered somewhat, and then a shift from blue to green occurs
with coablt oxide colourant.
Tom Buck ) tel: 905-389-2339
& snailmail: 373 East 43rd St. Hamilton ON L8T 3E1 Canada
(westend Lake Ontario, province of Ontario, Canada).
Ray Carlton on thu 29 oct 98
hi craig ...any chance of posting reitz green and the original recipe this
post began from??????
thanks
At 09:23 28/10/98 EST, you wrote:
>----------------------------Original message----------------------------
>>----------------------------Original message----------------------------
>>Hi,
>>I was wondering if anyone would like to explain how cobalt produces
>>green in this glaze instead of blue. I'd like to try is alter it to be a
>>little more fluid, but don't know how to change the recipe without
>>losing the green. Any comments on it's safety/durability?
>
>
>Hello:
>
>The rutile which contributes some titanium is influencing the green. This
>usually requires more than 1% rutile but this base seems to be real
>receptive to titania influence. High sodium glazes help develop this green
>and Reitz Green is very high in sodium.
>
>It's a durable glaze with plenty of alumina and silica but the high sodium
>content from the Neph Sy makes this a real crazer and it will leach cobalt.
>How much cobalt? I don't know, and you'll have to test it to find out.
>I've used this glaze on several test pieces and have seen it craze on a
>balanced cone 10 porcelain. It's a beautiful dark green matt. Lovely
>surface and does outrageous stuff with colored porcelain slips.
>
>The receipe I have uses EPK instead of Ball Clay so it's a bit more
>refractory than the receipe that you are using. You might try replacing
>all, or some of the Petalite with Spodumene to raise the level of lithium
>and produce a stronger melt. You could also raise the Gerstley Borate a bit
>instead of messing with the Petalite. When you get what you want,
>recalculate the glaze to determine the balance of the glass. Petalite is
>contributing the lions share of silica to this glaze and that's something to
>be aware of.
>
>regards, Craig Martell-Oregon
>
cheers Ray Carlton
McMahons Creek Victoria Australia
Michael Banks on fri 30 oct 98
---------------------------Original message----------------------------
>Hi,
>I was wondering if anyone would like to explain how cobalt produces
>green in this glaze instead of blue. I'd like to try is alter it to be a
>little more fluid, but don't know how to change the recipe without
>losing the green. Any comments on it's safety/durability?
>Reitz Green Matt:
>70 Neph Sy
> 5 Whiting
> 2 Gerstley Borate
>15 Petalite
> 8 Ball Clay
>Add:
> 1 Cobalt Carb
> 1 Rutile
>
>Thanks,
>Sylvia Mondloch
One way of looking at it, is that the rutile yellows the glaze and when
combined with the blue of cobalt, (yellow+blue=green) gives green. The high
expansion of this glaze (obviously craze prone) could be tackled by
replacing the Neph Sy with Potash Feldspar plus Spodumene by molar
reformulation.
Michael
Michael Banks
Nelson
mjbanks@clear.net.nz
muddpie on fri 30 oct 98
Mark, could you please tell us what cone this glaze is?? I have been
looking for a matte green, and can one (or two) of the glaze guru's out
there tell me if it would be food safe??.
thanks so much to all!!
JuliE in Michigan
Mark Mondloch wrote:
> ----------------------------Original message----------------------------
> Hi,
> I was wondering if anyone would like to explain how cobalt produces
> green in this glaze instead of blue. I'd like to try is alter it to be a
> little more fluid, but don't know how to change the recipe without
> losing the green. Any comments on it's safety/durability?
> Reitz Green Matt:
> 70 Neph Sy
> 5 Whiting
> 2 Gerstley Borate
> 15 Petalite
> 8 Ball Clay
> Add:
> 1 Cobalt Carb
> 1 Rutile
>
> Thanks,
> Sylvia Mondloch
>
> --
> Mark & Sylvia Mondloch
> Silver Creek Pottery & Forge
> W6725 Hwy 144
> Random Lake, WI 53075
>
> mondfam@execpc.com
> http://www.execpc.com/~mondfam
Mark Mondloch on sat 31 oct 98
Hi,
Thanks for the reply. I guess I expected the lithium was important but I had
thought of the rutile as more just a modifier. I think when I tryed a couple tes
and lost the green, I was probably changing too much. I'll try decreasing the cl
a bit and increasing the soak in my firing. Thanks again, Sylvia
Alexander Solla wrote:
> ----------------------------Original message----------------------------
> Sylvia-
> Green from cobalt is actually intimately related to the use of rutile
> in this glaze.
> If you want to keep the green but want it to be more fluid try increasing the
> whiting content a bit or decreasing the ball clay a bit.
> You could also play around with different bases and keep the colorants the sam
> ie. find your favorite glaze and try the cobalt and rutile combo and see
> what you think of that color.
> I will caution though, that part of the reaction is also caused by
> the lithium in the petalite... that in combination with the cobalt and ti and
> iron all add up. So, play with it, test it and try something else.
>
> ALex Solla
--
Mark & Sylvia Mondloch
Silver Creek Pottery & Forge
W6725 Hwy 144
Random Lake, WI 53075
mondfam@execpc.com
http://www.execpc.com/~mondfam
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