Alisa Liskin Clausen on tue 28 feb 06
cone 6, oxidation, General
_____
Dear Clayart
These tests are a series of percents and combinations of opacifiers in
different transparent bases. All of the test tiles have three lines of
color painted on them,
Cobalt Oxide wash, a Cobalt blue under glaze and a line of Red Iron Oxide
wash.
The purpose of these tests was to see how and how much the opacifiers in
percents and combinations would opacify the base glazes, if they change the
texture of the glaze and how they cover, mute or change the color of the
underlying oxides washes and under glazes.
In general, the tests showed results very similar to the text read in Hamer
and Hamer and other sources. It is exciting to see my own tests that
support the text.
Titanium, although not as much as an opacifier as Zircopax or Tin, produced
the most interesting color responses with Cobalt.
In tests where Zircopax was used to opacify the bases Tony Hansen's 20 x 5,
Alisa's Dolita Clear and Mike Bailey's Shiny Clear,
pink crystals formed on the Cobalt Oxide wash.
I cannot find any text to tell me why this happened. I have never seen them
before in my firings. I would be very happy if someone could help me
understand why this happened.
This would be a good time for me to underline how important I think it is to
both read, engage in dialogue and test. The first two gives a logical idea
of
where to start with testing, and tests show us where to select, read more
and go further.
Best regards,
Alisa in Denmark
Alisa Liskin Clausen on tue 28 feb 06
cone 6, oxidation
Glaze test for opacity and color response in 5 transparent bases, cone 6,
oxidation.
Glaze are tested on white midrange stoneware fired in electric oxidation to
1220c. (2228f)
Firing ramp with an electric controller is:
100c p/h to 600c (212f - 1112f)
150c p/h to 1140c (302f - 2084f)
80c p/h to 1220c (176f - 2228f)
15 min. soak
cool down max. to 900c (1652f)
Hold 1 hour
Shut off kiln
Note: All raw materials are measured up or down to the nearest half decimal.
Colorants or additives to a 100 gram test batch are measured in percent to
the 100 gram test batch.
Frit 3134 has been substituted for a local high Boron Frit in side by side
testing with no visible differences.
The opacifiers used are Tin Oxide, Zink Oxide, Titanium Oxide, Zircopax and
combinations of these.
Tin tended to give a creamy white opacity.
Zircopax gives a harder, sharper white, like bathroom porcelain.
Zinc mostly did not opacify the clear bases but acted as a flux and shined
up the bases.
Titanium Dioxide gave the most interesting color response to the painted
oxides, without much opacity.
In all of the tests where the glaze contained Zinc, the stripe of Cobalt
blue under glazed noticeably fumed pink. This validates again, the earlier
tests I made, demonstrating fuming by under glazes in glazes containing Tin.
Titanium produced green from Cobalt Oxide.
Below is a list of the bases tested and the results of each added opacifier.
1.
20 x 5 Clear Base, by Tony Hansen, ^6, oxidation.
20 Frit 3134
20 EPK
20 Silica
20 Custer Spar
20 Wollastonite
Base, transparent, gloss. Oxides showed true to color.
10 Zinc, transparent gloss, oxides showed true to color.
10 Zircopax, bright white gloss, Cobalt strong blue, under glaze grayish,
RIO is covered and shows grayish.
10 Tin, softer white gloss, Cobalt is strong, under glaze is lighter blue
and iron is visible but grayish.
5 Titanium, transparent gloss, slightly creamy color, cobalt strong, under
glaze clear, RIO brown and clear. Not much opacity.
5 Tin, 5 Zircopax, bright white gloss, cobalt is broken and mottled, under
glaze almost lost and iron is covered.
10 Titanium, white gloss, Cobalt is even more broken and pebbly, under glaze
and RIO are mostly covered.
5 Tin, creamy white gloss, Cobalt is strong, under glaze is a light blue,
RIO is grayish to covered.
2.
Alisa's Dolita Clear, Silk Mat, cone 6 oxidation. (named for Dolomite and
for a person I like as much as this glaze)
27 Frit 3134
30 EPK
18 Silica
10 Ball Clay
15 Dolomite
Base, transparent, silk mat, Cobalt is true, under glaze is slightly muted,
and RIO is brown.
10 Zinc, shinier white semi gloss, Cobalt is true, under glaze is slightly
bluer than above and RIO is brown, no opacifty.
10 Zircopax, bright white semi mat, Cobalt true, under glaze slightly greyer
and paler and RIO is covered.
10 Tin, Toast colored semi gloss, both blues are grey and RIO is brown.
5 Titanium, grey blue silk mat, slightly white crystals, Cobalt is muted,
under glaze is green with yellow specs and RIO is slightly covered.
5 Titanium, 5 Zircopax, silk mat, medium white with toast color edges.
Cobalt is muted, under glaze is muted and RIO is visible and brown.
5 Tin, cream white silk mat, Cobalt is true, under glaze is slightly muted
and RIO is true and brown.
10 Titanium, grey blue and yellow glaze, Cobalt is blue and green, under
glaze is green with yellow specs, iron is visible with yellow specs.
3.
Mike Bailey's Shiny Clear, ^6 oxidation.
43 Soda Spar
5 China clay
2 Bentonite
22.5 Whiting
6 Zinc Oxide
21.5 Silica
Base, transparent, gloss. Oxides and under glaze showed true.
10 Zinc, no noticeable difference from base
10 Zircopax, bright white gloss, Cobalt shows through with distinct pink
crystals where oxide is most saturated. Under glaze is very muted and iron
is covered.
10 Tin, shiny, gloss, soft white. Oxides and under glaze are muted. A pink
halo around under glaze stripe.
5 Titanium, shiny, clear gloss. Cobalt Oxide is green, under and RIO are
visible.
5 Titanium, 5 Zircopax, shiny, gloss bright white. Oxide and under glaze
are slightly muted.
5 Tin, shiny, soft white gloss, Cobalt and RIO are slightly muted and under
glaze has a weak pink halo.
10 Titanium, transparent, gloss. Cobalt is speckled with green, RIO and
under glaze show true.
4.
Emmanuel Cooper's Water Clear, ^6 oxidation.
40 Soda Spar
20 Whiting
8 Ball Clay
5 China Clay
27 Silica
Base, milky, transparent gloss. Oxides and under glaze are visible.
10 Zinc, transparent, shiny gloss. Oxides and under glaze are visible.
10 Zircopax, whiter glaze, but not a hard white. Oxides and under glaze
slightly muted.
10 Tin, milky, transparent gloss. Oxides and under glaze slightly muted,
under glaze fumed.
5 Titanium, transparent gloss. Oxides and under glaze showed true.
5 Titanium, 5 Zircopax, soft white gloss. Oxides and under glaze slightly
muted.
5 Tin, milky white gloss. Oxides show true, under glaze has a pink halo.
10 Titanium, white gloss. Cobalt shows true, RIO and under glaze are muted.
5.
Grace's B Base, cone 6, ox.
20 Frit 3134
20 Dolomite
20 Soda Spar
20 Ball Clay
20 Silica
(recipe calls for 5% Tin, which was omitted in this base, but used an
addition for one test)
5 Tin, soft white semi gloss. Oxides and under glaze are substantially
muted.
10 Tin, same as above.
5 Tin, 5 Zircon, milky white semi gloss with almost no opacity.
10 Zircon, slightly more opacity than above.
I was surprised that 5 Tin Oxide appears to have opacified this base more
than double that oxide or Zircopax. Could also be application of 5 Tin was
thicker.
Additional tests
EZ Clear, cone 6, ox.
50 Frit 3134
20 Kaolin
20 Silica
Base, shiny, transparent gloss, Oxides and under glazed showed true.
10 Zircopax, shiny, stark white. Oxides very muted, under glazed shows as a
pebbly stripe with diffused edges.
EZ Clear, cone 6, ox. Reversed Kaolin and Silica percents
50 Frit 3134
30 Kaolin
20 Silica
Base, shiny, transparent gloss. Oxides and under glaze showed true. Glaze
is crazed
10 Zircopax, shiny, sharp white gloss. Oxides very muted, under glaze shows
under glaze as a pebbly blue stripe with diffused edges. No visible
crazing.
Best regards
Alisa in Denmark
Alisa Liskin Clausen on wed 1 mar 06
cone 6, oxidation
Steve wrote
>
>I haven't found pink fuming from
>cobalt overglazes in the presence
>of zinc (though I've only done it
>once or twice) but I have seen a
>hint of it in a partial-zinc glaze
>that has cobalt as a colorant.
>
>
in response to my post
>>
>> In all of the tests where the glaze contained
>> Zinc, the stripe of Cobalt
>> blue under glazed noticeably fumed pink. This
>> validates again, the earlier
>> tests I made, demonstrating fuming by under
>> glazes in glazes containing Tin.
Hi Steven
I sent a correction to this mistake in the paragraph, where I wrote Zinc,
and as the last sentenced shows, meant Tin. But that is not as apparent
as I thought, because it is easily misread that now I have had fuming with
under glazes with both Zinc and Tin. Fact is, I have had fuming with all
of bases with Tin where the under glaze is applied.
What about those bright pink crystals in the Cobalt wash over the bases
with Zircopax? Do you have any ideas about those? They are very pretty
but I am not sure I will always want them.
I will post photos as soon as I can get my butt outside long enough for
the job, March 1 and all the Snow Drops of hope are lost under a few
inches of snow. The good news is, that they will miraculously be there
when the snow melts.
Hope it is a great NCECA. We will meet in Louisville, I hope.
Regards from Alisa in Denmark
Ivor and Olive Lewis on thu 2 mar 06
Dear Alisa Liskin Clausen,=20
Do not be surprised at getting a pink colouration with Cobalt oxide. One =
of the natural ores, "Erythrite" is a pink amorphous substance and many =
Cobalt salts which are blue in the solid state change to pink in the =
presence of water vapour.
To understand why colours appear when Transitional Metals are used as =
colouring agents requires a deeper understanding of the way coordination =
complexes form as each metallic atom surrounds itself with more =
electrons than are needed to satisfy the exchange of valency electrons.=20
I consider myself fortunate to benefit when Nature behaves in these =
mysterious ways.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Steve Slatin on fri 3 mar 06
Ivor --
Erythrite is pink -- and so is roselite -- but
they're both arsenates. And monoclinic. The
cobalt carbonates are trigonal, AFAIK. But we
shouldn't have either arsenates or carbonates
in that glaze, I'd think. That pink's an
elusive guy.
-- Steve S
--- Ivor and Olive Lewis
wrote:
> Dear Alisa Liskin Clausen,
> Do not be surprised at getting a pink
> colouration with Cobalt oxide. One of the
> natural ores, "Erythrite" is a pink amorphous
> substance and many Cobalt salts which are blue
> in the solid state change to pink in the
> presence of water vapour.
Steve Slatin --
In watermelon sugar the deeds were done and done again
as my life is done in watermelon sugar.
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Ivor and Olive Lewis on sun 5 mar 06
Dear Steve Slatin,=20
Pink colouration in Cobalt compounds is not unusual. In fact it is well =
know and is used as a marker for Moisture. Anhydrous Cobalt salts tend =
to be Blue. As they adsorb moisture they change to Pink. This is =
reversible. It was common practice to keep a filter paper that had been =
soaked in Cobalt Chloride and then dried in a desiccating jar.
Big problem is understanding why we perceive colour. As I said in my =
previous post, there is a need to understand the relationship each =
Cobalt atom has with its neighbours, the way they share out their =
electrons and the way electrons selectively adsorb and release energy at =
specific wavelengths.
Think about Common Salt. Normally we see this as a white substance. But =
if we energise it by heating it in a Bunsen flame we see a vivid yellow. =
Heat is changed into visible light.Transition elements adsorb invisible =
wavelengths and convert them into visible parts of the spectrum.
The only way to solve this problem is to is to analyse the glaze and =
determine its composition. I think the usual process is via X-Ray =
Diffraction.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
earlk on sun 5 mar 06
On Sun, 2006-03-05 at 17:24 +1030, Ivor and Olive Lewis wrote:
> Big problem is understanding why we perceive colour. As I said in my
> previous post, there is a need to understand the relationship each
> Cobalt atom has with its neighbours, the way they share out their
> electrons and the way electrons selectively adsorb and release energy
> at specific wavelengths.
I have seen descriptions of glass/glaze that
describe chains of silica molecules linked
together by aluminum atoms but have always
wondered how everything else in a glaze fits
into this structure. If we knew then maybe
we could answer questions such as why copper
does not leach appreciably until a certain
concentration is reached. Is this because there
are "copper holding cells" in the structure.
Once these cells are completely filled does the
additional copper just float around free and is
therefore easily leached? Wouldn't it be nice
to know?
> The only way to solve this problem is to is to analyse the glaze and
> determine its composition. I think the usual process is via X-Ray
> Diffraction.
My understanding of X-ray diffraction analysis
is that it depends on a repetative structure to
be useful. In a semi-amorphous material like
glass I can see that this technique would have
limited use. But how about the technique that
IBM developed, scanning tunnelling microscopy,
where they run a one-atom needle point over a
surface and measure the electrostatic force
fields. This allows them to detect the location
of individual atoms. That might be useful.
A link to more about this technique:
http://www.deutsches-museum.de/ausstell/meister/e_rtm.htm
earlk
bothell, wa, usa
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