Wanda Holmes at Alistia on sun 25 nov 01
I am a tilemaker. I want to use Pete Pinell's Weathered Bronze Green on the
floor of a covered patio, but it scratches too easily. So, I decided to use
Ian Currie's grid method to adjust it towards a harder surface without
getting too far away from the satin matte finish.
The original recipe falls at position #27 in the grid (unity formulas
below), so I fired tests of positions 17, 18, 22, & 23. The glazes at
positions 18 & 23 are harder, but only glaze #22 remotely resembles the
original color. Here's the chemistry:
Original recipe:
Na2O .36 Al2O3 .56 SiO2 2.98 Al:SI Ratio 5.28
K2O . 11
MgO .01
CaO .02
Li2O .05
SrO .46
In each of the new recipes, the flux values remains the same. The Al, Si,
and Al:Si Ratio values are:
Recipe 22 - Al2O3 .65 SiO2 3.19 Al:Si Ratio 4.90
Recipe 23 - Al2O3 .66 SiO2 4.13 Al:Si Ratio 6.28
Recipe 17 - Al2O3 .75 SiO2 3.42 Al:Si Ratio 4.56
Recipe 18 - Al2O3 .76 SiO2 4.39 Al:Si Ratio 5.79
Recipe 22 has a noticeably altered color, but is similar to the original.
Recipes 17, 18, & 23 are very different - a dull kakhi color rather than
green. I graphed these values and the thing that stands out is that the
amount of SiO2 is nearest the original value in recipe #22, the one with the
color nearest the original. I'm pretty new at glaze chemistry. Can the
amount of silica have such a profound impact on the color response or am I
overlooking something else?
These tests were fired in the same kiln load on the same clay. In fact the
test tiles came out of the same bisque load.
Electric kiln with Envirovent on throughout firing and cooling. Cone 6 tip
completely down and cone 7 just starting to bend.
The firing schedule used was:
176 degrees F to 352
284 1200
212 1832
284 2052
108 2232 hold for 0.5 hrs.
Any insight anyone can offer will be most appreciated.
Thanks,
Wanda
Cindy Strnad on sun 25 nov 01
Hi, Wanda.
This isn't very scientifically profound, but I
wonder if you got the glaze thick enough? For me,
Weathered Bronze Green is a kind of dull iron gray
where thin.
Cindy Strnad
Earthen Vessels Pottery
RR 1, Box 51
Custer, SD 57730
USA
cindy@earthen-vessels-pottery.com
http://www.earthen-vessels-pottery.com
Paul Lewing on mon 26 nov 01
Wanda, there is one other number I think you're overlooking. The Al:SI
ratio of #27 and #22 are also the closest to each other. I'd suggest
another series of tests- keep the flux balance the same and keep the ratio
the same, just add both alumina and silica in that proportion. Maybe make
up batches that add about .05 Al and .25 Si for each increment of testing.
I'd bet that the glaze would get harder, but at some point the color would
change. Just below that would be the hardest variation on this formula that
would still stay that color. Let us know what happens. it's an interesting
problem.
Also, I must commend you on an excellent post. Not just an interesting
problem, but you did your homework first, and you laid out all the relevant
data very clearly and concisely. Keep this up and we expect to see you here
answering other people's glaze questions before long.
Paul Lewing, Seattle
on 11/25/01 6:41 PM, Wanda Holmes at Alistia at wanda.holmes@ALISTIA.COM
wrote:
> The original recipe falls at position #27 in the grid (unity formulas
> below), so I fired tests of positions 17, 18, 22, & 23. The glazes at
> positions 18 & 23 are harder, but only glaze #22 remotely resembles the
> original color. Here's the chemistry:
>
> Original recipe:
> Na2O .36 Al2O3 .56 SiO2 2.98 Al:SI Ratio 5.28
> K2O . 11
> MgO .01
> CaO .02
> Li2O .05
> SrO .46
>
> In each of the new recipes, the flux values remains the same. The Al, Si,
> and Al:Si Ratio values are:
>
> Recipe 22 - Al2O3 .65 SiO2 3.19 Al:Si Ratio 4.90
> Recipe 23 - Al2O3 .66 SiO2 4.13 Al:Si Ratio 6.28
> Recipe 17 - Al2O3 .75 SiO2 3.42 Al:Si Ratio 4.56
> Recipe 18 - Al2O3 .76 SiO2 4.39 Al:Si Ratio 5.79
>
> Recipe 22 has a noticeably altered color, but is similar to the original.
> Recipes 17, 18, & 23 are very different - a dull kakhi color rather than
> green. I graphed these values and the thing that stands out is that the
> amount of SiO2 is nearest the original value in recipe #22, the one with the
> color nearest the original. I'm pretty new at glaze chemistry. Can the
> amount of silica have such a profound impact on the color response or am I
> overlooking something else?
Chris Schafale on mon 26 nov 01
Wanda,
The short answer is yes. The amount of silica in a glaze can have
a profound effect on color response in certain glazes. I've seen the
same thing with a copper blue, where the blue completely goes
away when the silica goes up one notch on the Currie grid. Sad,
because this prevents you from adding silica to reduce crazing, etc.
Chris
Date sent: Sun, 25 Nov 2001 20:41:59 -0600
Send reply to: Ceramic Arts Discussion List
From: Wanda Holmes at Alistia
Subject: Glaze Mystery aka Why the heck did this happen???
To: CLAYART@LSV.CERAMICS.ORG
> I am a tilemaker. I want to use Pete Pinell's Weathered Bronze Green on the
> floor of a covered patio, but it scratches too easily. So, I decided to use
> Ian Currie's grid method to adjust it towards a harder surface without
> getting too far away from the satin matte finish.
>
> The original recipe falls at position #27 in the grid (unity formulas
> below), so I fired tests of positions 17, 18, 22, & 23. The glazes at
> positions 18 & 23 are harder, but only glaze #22 remotely resembles the
> original color. Here's the chemistry:
>
> Original recipe:
> Na2O .36 Al2O3 .56 SiO2 2.98 Al:SI Ratio 5.28
> K2O . 11
> MgO .01
> CaO .02
> Li2O .05
> SrO .46
>
> In each of the new recipes, the flux values remains the same. The Al, Si,
> and Al:Si Ratio values are:
>
> Recipe 22 - Al2O3 .65 SiO2 3.19 Al:Si Ratio 4.90
> Recipe 23 - Al2O3 .66 SiO2 4.13 Al:Si Ratio 6.28
> Recipe 17 - Al2O3 .75 SiO2 3.42 Al:Si Ratio 4.56
> Recipe 18 - Al2O3 .76 SiO2 4.39 Al:Si Ratio 5.79
>
> Recipe 22 has a noticeably altered color, but is similar to the original.
> Recipes 17, 18, & 23 are very different - a dull kakhi color rather than
> green. I graphed these values and the thing that stands out is that the
> amount of SiO2 is nearest the original value in recipe #22, the one with the
> color nearest the original. I'm pretty new at glaze chemistry. Can the
> amount of silica have such a profound impact on the color response or am I
> overlooking something else?
>
> These tests were fired in the same kiln load on the same clay. In fact the
> test tiles came out of the same bisque load.
>
> Electric kiln with Envirovent on throughout firing and cooling. Cone 6 tip
> completely down and cone 7 just starting to bend.
>
> The firing schedule used was:
> 176 degrees F to 352
> 284 1200
> 212 1832
> 284 2052
> 108 2232 hold for 0.5 hrs.
>
> Any insight anyone can offer will be most appreciated.
>
> Thanks,
> Wanda
>
> ______________________________________________________________________________
> 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.
>
Light One Candle Pottery
Fuquay-Varina, North Carolina, USA
(south of Raleigh)
candle@intrex.net
http://www.lightonecandle.com
Ruth Ballou on mon 26 nov 01
Both alumina and silica can have profound effects on color response. This
is one of the variables that the grid shows off so well. The samples you've
chosen are moving up the alumina baseline as well as the silica baseline,
so the change in both is having an effect.
Pete Pinnell recently wrote in about Weathered Bronze Green. Might help.Try
the archives.
One other thought..... have you tried putting a thin coat of clear glaze
over the WBG. Other glazes have been helped by this.
Ruth Ballou
>I am a tilemaker. I want to use Pete Pinell's Weathered Bronze Green on the
>floor of a covered patio, but it scratches too easily. So, I decided to use
>Ian Currie's grid method to adjust it towards a harder surface without
>getting too far away from the satin matte finish.
>
>The original recipe falls at position #27 in the grid (unity formulas
>below), so I fired tests of positions 17, 18, 22, & 23. The glazes at
>positions 18 & 23 are harder, but only glaze #22 remotely resembles the
>original color. Here's the chemistry:
>
>Original recipe:
>Na2O .36 Al2O3 .56 SiO2 2.98 Al:SI Ratio 5.28
>K2O . 11
>MgO .01
>CaO .02
>Li2O .05
>SrO .46
>
>In each of the new recipes, the flux values remains the same. The Al, Si,
>and Al:Si Ratio values are:
>
>Recipe 22 - Al2O3 .65 SiO2 3.19 Al:Si Ratio 4.90
>Recipe 23 - Al2O3 .66 SiO2 4.13 Al:Si Ratio 6.28
>Recipe 17 - Al2O3 .75 SiO2 3.42 Al:Si Ratio 4.56
>Recipe 18 - Al2O3 .76 SiO2 4.39 Al:Si Ratio 5.79
>
>Recipe 22 has a noticeably altered color, but is similar to the original.
>Recipes 17, 18, & 23 are very different - a dull kakhi color rather than
>green. I graphed these values and the thing that stands out is that the
>amount of SiO2 is nearest the original value in recipe #22, the one with the
>color nearest the original. I'm pretty new at glaze chemistry. Can the
>amount of silica have such a profound impact on the color response or am I
>overlooking something else?
>
>These tests were fired in the same kiln load on the same clay. In fact the
>test tiles came out of the same bisque load.
>
>Electric kiln with Envirovent on throughout firing and cooling. Cone 6 tip
>completely down and cone 7 just starting to bend.
>
>The firing schedule used was:
>176 degrees F to 352
>284 1200
>212 1832
>284 2052
>108 2232 hold for 0.5 hrs.
>
>Any insight anyone can offer will be most appreciated.
>
>Thanks,
>Wanda
>
>______________________________________________________________________________
>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.
| |
|
