|
William S P
I R A L _______________________ 206 White Oak Drive Austin TX 78753 |
512-339-7610 |
Melstrom S T
U D I O _______________________ www.handspiral.com william@handspiral.com |
January 3, 2010
Silver Nitrate in Crystalline Glazes
THE SILVER NITRATE MANIFESTO
William Melstrom
June 8, 2006
I do not recommend that anyone but the most experienced crystalliers experiment with silver nitrate. If you have a great deal of control over your crystalline glazes, and have a thorough understanding of how parameters such as time, temperature, glaze thickness and composition, etc., effect crystallines, and if you have a high threshold for failure and aggravation, then silver nitrate’s use as a colorant might be worth pursuing. For all other crystalliers, your time and money would be much better spent perfecting your existing glazes. In short, I do not recommend that you use silver nitrate.
Some of the problems
involved with silver nitrate include:
1) It is expensive. In
the June/July 2006 issue of Ceramics Monthly, Westerwald Chemicals
advertises 25 grams of silver nitrate for $15, and 1 pound of copper carbonate
at $4. This makes silver nitrate 65
times more expensive than copper carbonate.
In the same issue of CM, U.S. Pigment Corporation advertises
silver nitrate for $150 per pound and high purity red iron oxide for $3 per
pound. That makes the silver nitrate 50
times more expensive than the red iron oxide.
2) When mixed with water and exposed to light, silver nitrate is
an extremely powerful oxidant. It will
permanently stain everything that it comes in contact with black (silver
nitrate is the black pigment used in many fine black and white photographic
prints). It will oxidize and destroy
brushes made with natural materials. It
will stain your skin black (but not permanently, it disappears as your
epidermis exfoliates).
3) It is very hard to achieve satisfactory results with silver
nitrate. Effects are mercurial and vary
from firing to firing. Acceptable
results almost always require additional post-firing methods such as reducing
or striking (see my web site page on post firing techniques: http://www.handspiral.com/Post_Fire.htm
for more information).
Did I mention that I don’t recommend that you experiment with silver nitrate? I did? Good.
I mix two parts of
water to one part of silver nitrate, by weight, and I brush it onto unfired
ware that has been pre-glazed with my base crystalline glaze. I have a dedicated mixing bowl, which I
never wash, thus preventing wasting the expensive silver nitrate. I use old, spent sable mop brushes that I
would throw out otherwise. A brush might
last for about ten to twenty sessions before it disintegrates. It is possible that certain synthetic
brushes might hold up longer, but I have not tried synthetics yet, and I like
the liquid-holding properties of sable.
I brush a single coat onto the piece.
It is a lot like just brushing plain water onto the ware – silver
nitrate completely dissolves in water, yielding a colorless liquid. I try to apply the single coat of silver
nitrate as evenly as possible. A bit of
overlapping, or a bit of small areas that are left bare, are not a
problem. Due to the fact that a lot of
the silver nitrate will volatize and fume the kiln, and because of the flowing
nature of crystalline glazes, you will end up with an acceptably evenly coated
piece.
Some people add their
silver nitrate to their base glaze.
This works, but I don’t like this method for three reasons:
1) You run the risk of staining, and perhaps even damaging your
equipment, sieves, containers, etc.
2) There will be inevitable waste of the expensive silver
nitrate when you wash your mixing equipment.
3) Silver nitrate is an extremely powerful glaze
thickener. You have to see it to
believe it. You will probably add about
50% more water than normal to your batch to get a consistency that appears
normal. This could lead to application
issues.
If you do add the
silver nitrate directly to your base, I suggest trying 5 to 10%.
Silver nitrate
volatilizes at typical macro-crystalline zinc-silicate glaze temperatures. It will coat all the surfaces within your
kiln. It will then re-volatilize during
subsequent firings, affecting, perhaps adversely, ware in those firings.
I do all of my work
with silver nitrate in a relatively small kiln that is suited to
experimentation. I have noticed some
degradation of the soft brick in this kiln.
The degradation occurs mainly at the top of the kiln, which I leave
cracked until I reach about 1000C -- I assume it is caused by silver nitrate
fumes escaping the kiln. A coating of
ITC would probably help a great deal, but I have not tried ITC. A kiln vent would probably eliminate a lot
of the soft brick degradation, and would slow the coating of the kiln
contents. However, I have little doubt
that the silver nitrate fumes would quickly oxidize, corrode and destroy a kiln
vent. So, if your kiln has one, leave
the fan off, and crack your kiln until you reach 1000C.
Have I said that I don’t recommend that you experiment with silver nitrate? Just checking.
If all goes well, and
you successfully resolve application issues and determine a firing schedule
that yields nice crystals, you are now only half way home. You might have very nicely shaped crystals,
but typically they will be white on white.
There might be touches, or even large areas with color, but typically
that color will be a sort of brownish-burgundy. Although not very attractive, the burgundy coloration means that
you are on the right track. Now, you
must develop the color, either through striking or reducing (see my web site
page on post firing techniques: http://www.handspiral.com/Post_Fire.htm
for more information).
Striking silver
nitrate pieces will ideally result in an incredibly beautiful Welch’s grape
purple. However, striking will
necessitate a completely new series of experiments, until you find temperatures
and schedules that work for you. It is
worth mentioning that very, very occasionally, I get the Welch’s purple from an
initial crystalline firing. It usually
isn’t intense enough, and I almost always go ahead with a post-fire
technique. I have no idea why a first
firing can yield either purple, or burgundy, or nothing, when I do everything
exactly identically. It is very
perplexing.
Alternatively, you
can reduce your silver nitrate work. I
reduce in a simple, dedicated, natural gas kiln. People who have the capability to reduce during their initial
crystalline firing may do it that way.
The good news about reducing is that it is usually successful, and if it
isn’t, you can just keep re-firing in reduction until you get a result that you
like.
Heavy, prolonged
reduction with a target temperature of from about 760 to 830C results in pure
silver crystals on a pure silver background.
Cooler temperatures and/or mild reduction yield a variety of attractive
golds, bronzes, brasses and iridescent effects. But beware. You can also get
some very strange results. Often the
background becomes very matte.
Sometimes this is appealing, sometimes it is not. The crystals themselves will always lose
their luminescent quality – they will no longer look like they are lit-up from
within, and the quality of looking underneath the surface of the crystal, into
the glaze will be lost. Again,
sometimes this is appealing, sometimes it is not. All of these colors and effects are very serendipitous and
mercurial, and are very hard to control or duplicate.
The final step in
making reduced silver crystals is polishing.
I have tried a number of polishes, and I highly endorse Hagerty
Silversmith’s Polish. By all means,
avoid Tarn-X Tarnish Remover. If your
glaze did not contain enough silver nitrate – perhaps your concentration wasn’t
strong enough, or too much fumed and escaped the glaze, or, more likely, you
did not reduce strongly or long enough – it is very likely that your silver
layer will be so thin that you will polish it right off. It’s just one final opportunity to screw up
and ruin your work.
I strongly recommend
that you don’t try using silver nitrate.
If, after reading this, you agree with me, then I have done my job. I have just saved you untold hours of aggravation,
grief and disappointment, not to mention all of the money that I have saved you
in silver and lost work. You can repay
me by buying one of my silver nitrate works.
If you can’t afford a big piece, I offer some very nice, very reasonable
small pieces. This is not charity. You
will get a beautiful and unique piece of art that will probably be worth many
times what you paid for it after I die.
If you do decide to
continue your explorations of silver nitrate as a crystalline glaze colorant,
the above information will still save you untold hours of aggravation, grief
and disappointment, and a great deal of lost work. You too can repay me by buying one of my silver nitrate works.
(Note to my friends
about the last two paragraphs, and the whole general tone of this article: I cannot
tell you how many times people have written me hurried, grammer-less emails
asking for information that required long explanations. More than half of these people then don’t
even have the courtesy to write a simple “thanks.” So, I guess I was venting when I wrote that.)
Best Wishes,
William Melstrom
Addendum, February 5,
2007
Due to tarnishing
issues, I no longer am producing the “pure silver” look of reduced silver
nitrate. It is impossible to prevent
the pure silver surface from tarnishing. After a couple of re-polishings, the silver will be completely
removed. You will still be left with an
interesting piece, but with nowhere near the allure that the pure silver has.
I now suggest very
slightly re-oxidizing at the end of the reduction firing. This yields very unique oranges and yellows
that are stable.
Addendum, March 2,
2007
Silver nitrate and
CMC do not mix! But, it’s pretty cool
to see for yourself. Add a couple of
drops of silver nitrate solution to a couple of drops of CMC solution.
However, you can
brush silver nitrate solution on top of a CMC containing glaze that has
dried. That’s what I do.
I do not recommend
spraying the silver nitrate solution because you will loose the very expensive
silver nitrate in the overspray. And,
you risk damaging your spray equipment and your spray booth, especially the
exhaust fan, through oxidation.