Tom Buck on fri 4 sep 98
Bob Wicks:
I did some research on Raku Lustres (because I was intrigued) and
I learned some things. My original writeup appeared in UK's Ceramic
Review, issue 159 (Mar/Apr 96), a copy of which Tony Hansen has available
at his website, digitalfire.com/education/glaze.
The Tomato and Copper lustres, as usually formulated, will
always degrade with time. But as you say, using a clear sealant like an
acrylic will delay the onset of mud. However, if the buyer/owner places
the piece in a bright room in direct sunlight, the energetic photons will
penetrate into the glaze and alter the copper/iron reds or copper metal
and change them into black oxides and thereby the pots will lose their
orignal colour and sheen. The bright penny copper lustre is especially
susceptible to this and no amount of reformulating will change its
mutability. Just keep it in a cool softlit room and it may last for years.
However, the Tomato Lustre, by reformulating, will become quite
stable to energetic photons. I placed one test plate outside all summer
and it survived quite well, just a very slight darkening.
The gold lustre survived the summer but it did darken somewhat,
and lost part of its original bright yellow colour. But I judged the
reformulation to be acceptable.
As for Copper Sand Lustre, the original recipe was quite
deficient in silica, and glass made of P2O5 and B2O3 doesn't have the
stability of bottle glass (soda-lime silicate). The recipe can be adjusted
but obtaining the textured surface is a separate matter from glass
stability. The revised recipe gave a glaze stable to bright sunlight but
its texture and colour are altered to a degree and may not suit some
potters.
However, after my efforts with Raku Lustres, I am convinced that
stable Lustres can be achieved, and some interesting new effects may be
possible.
Good tests.
Tom Buck
) tel:
905-389-2339 & snailmail: 373 East 43rd St. Hamilton ON L8T 3E1 Canada
(westend Lake Ontario, province of Ontario, Canada).
Tom Buck on sat 5 sep 98
Bob:
Perhaps the following will make sense; I hope so. As components of
electromagnetic radiation, Photons come in various energy levels. This is
what Handbook of Chemistry and Physics says in its definition section:
"Photon.-- A photon (or gamma-ray) is a quantum of electromagnetic
radiation which has a zero rest mass and an energy of h (Planck's
constant) times the frequency of the radiation. Photons are generated in
collisions between nuclei or electrons and in any other process in which
an electrically charged particle changes its momentum. Conversely photons
can be absorbed (i.e., annihilated) by any charged particle."
The fuss over the Ozone layer has made everbody aware of the
increase in ultraviolet radiation levels at ground level. In effect,
bright sunlight has a significant amount of UV photons which I call
energetic photons to make the distinction between Infra-red Photons and UV
Photons. UV photons will be absorbed by the surface atoms of a pot and if
those atoms are metastable (like in Cu red and Cu metal), the photons
will alter the charge on those atoms, Cu going from +1 to +2 or from 0 to
+1 to +2. The result is a change in colour by a radiation effect, not a
surface chemical effect.
This is what happens to Copper lustre especially, the bright penny
hue being downgraded to Copper Red/Black, a darkish tone. The Tomato Red
Lustre (Cu/Fe red/blue) is more stable and can absorb UV Photons without a
severe downgrading of colour; it just goes a bit darker. Gold lustre
suffers a lessening of yellow colour after long exposure to energetic
photons but remains a darkish gold. Copper Sand Lustre, the traditional
recipe, will undergo both colour and compositional changes that degrade
the glaze in unpredictable ways because the claybody will affect the
result.
The conclusion I offer: use reformulated Lustre Recipes (see my
article), and keep the pots in a cool subdued light room and all will be
well.
Good pots.
Tom Buck ) tel: 905-389-2339
& snailmail: 373 East 43rd St. Hamilton ON L8T 3E1 Canada
(westend Lake Ontario, province of Ontario, Canada).
Candone Wharton on sat 5 sep 98
Hi all,
I have been using my own Raku luster glazes for over 20 years and have had
little
or no changes with time. I have a really strong gold glaze which is nothing
more than 2% silver nitrate added to my base, this glaze resembles a low fire
luster and is a very stable glaze. It seems that by adding the silver nitrate
into the base and not spraying them onto the glaze stabilizes the luster.
The main change I have seen
is greying of the unglazed black surfaces when exposed to sunlight over a long
period of time which is explainable. As far as the gold and copper lusters,
I have pieces I made years ago and they shine like they were just pulled out
of the kiln.
Candone
Jim Cullen on tue 8 sep 98
Just to add my 2 cents.
I saw Candone's raku lustres at the ACC show at Navy Pier in Chicago and they
are absolutely beautiful. I didn't realize they were raku until I asked and
then I was doubly impressed. She has a look and brilliance in her pots that
are uniquely hers and wonderful by any standards. Now, if I could only express
myself better I'd tell you all what I really thought of her pots. They are
stunning.
Thanks Candone for sharing your art with the world.
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