Appendix B: Straightforward preparation of a gold ruby stain

The early literature provides many methods for preparing
the pigment, most of which seem relatively
cumbersome. (See Appendix D, below.) Here is a rapid and
straightforward synthesis that produces enough pigment
to provide 0.05% Au in a 100-gram test batch of
glaze. Doubling the amount of gold chloride provides
0.1% Au, and produces deeper color in the fired glaze.

“Step 0”: Before you start, it is helpful to
dissolve 1 gram of AuCl₃ in 12 grams of
distilled water. 1 gram of the resulting solution
contains approximately 50 milligrams of gold, which is
required in Step 2 of the preparation.

Step 1: Suspend 5 grams of Al(OH)₃ (Aluminum
Hydroxide, often inaccurately referred to as
“Alumina Hydrate”) in approximately 12 grams
of distilled water (the amount is not crucial) at room
temperature, with stirring. Other substrates may be used
in place of Al(OH)₃, but see Note 2, below.

Step 2: Continue stirring the resulting suspension, and
add 50 mg of gold in the form of an aqueous solution of
the chloride. If you are using a solution prepared as in
Step 0 above, you will require 1 gram.

Step 3: Add, dropwise, an aqueous solution of
SnCl₂ (Stannous Chloride), stirring with each
addition, until no further change in color is
observed. It is a good idea to add a slight excess, as
the change in color becomes progressively more difficult
to observe as the color darkens. Solid SnCl₂
can be used instead of a solution, but the solution is
more convenient.

The resulting suspension can be added directly to 95
grams of other materials to produce a 100-gram glaze
batch. (See Appendix C for an example recipe.)

Notes:

1. This preparation produces mauve stains. I have not
investigated further, but the colloidal gold colorant is
known to be capable of producing a surprisingly wide
range of colors, depending on conditions. The color
depends on the particle size, and possibly other
parameters.

2. The pigment can be deposited on a wide variety of
substrates. Aluminum hydroxide is convenient, as is
alumina, and the resulting color is satisfactory with
either. Kaolin is used in Hermann Seger’s
preparation, which is given in Appendix D, and
should work well in this preparation. Pigment deposited
on Nb₂O₅, however, did not produce
significant color in the fired glaze when I tested
it. Pigment deposited in an aqueous solution of
ZrOCl₂ has remained in suspension for several
years; I have not yet attempted to use it in a glaze.

I have not tried working with larger quantities, but I
have no reason to expect any problems with scaling.

Appendix C: Example test glaze, for [Orton] cone 9-11

The following glaze produces consistent mauve color with
0.05% or 0.1% Au (prepared as in Appendix A and added as
a stain), when fired to Orton cone 10 or 11 in a mildly
reducing atmosphere. When fired to cone 9 in air it
produces an extremely pale pinkish color.

Note: This recipe is merely a representative
testing formulation, and is not intended to be
prescriptive.

Kaolin            20g  (Any good primary kaolin; I use Super Standard Porcelain)
Petalite          30g
Wollastonite      25g
MgCO3              5g
Fusion Frit F-69  15g  (or Ferro Frit 3249)
Mauve Stain        5g  (plus small amounts of Au and Sn from preparation)

Total:           100g  (ignoring the Au and Sn)

Seger numbers for this glaze, as calculated by Insight:

Al2O3:  0.465
SiO2:   2.357
B2O3:   0.175
K2O:    0.010
Na2O:   trace
Li2O:   0.132
CaO:    0.582
MgO:    0.276
Fe2O3:  0.002
TiO2:   0.003

Appendix D: A late 19th or early 20th century example:
Hermann Seger’s preparation

“Very beautiful purple and rose tints are obtained
by introducing gold as a coloring metallic oxide
[sic]. A strong purple-red is prepared in the
following manner: Of pure white kaolin, best English
china clay, 90 parts [sic] are worked up in water
by boiling and sieving; then 10 grams of gold are
dissolved in a mixture of nitric and hydrochloric acids,
the solution being freed from excess of acid as much as
possible by evaporation on the water-bath. The gold
solution is then mixed with the clay slip, sodium
carbonate is added till the liquid is distinctly
alkaline, and after an addition of about 20 grams of
grape-sugar the mixture is boiled strongly for half an
hour, water being added to maintain the same
volume. Thus a dark purple colored mass is obtained,
which must be washed and then dried and ignited at a
heat not exceeding silver-melting heat. It will in this
way assume a somewhat lighter color. A second washing
after the grinding of the color is desirable since the
first washing is never as complete as is necessary.

“A beautiful rose color is thus obtained from

98 parts [sic] of white porcelain clay

2 grams of gold”

Notes:

1. The melting point of silver is just under 962° C.

2. This method, while somewhat annoying to follow, is
not actually unreasonable. Gold chloride can be
purchased, which eliminates the need for strong acids;
potassium carbonate (pearl ash) can be used
interchangeably with sodium carbonate (washing soda);
fructose can be substituted for grape-sugar; it is
convenient to heat the suspension in a microwave oven;
and the addition of even a very small amount of
SnCl₂ prior to the addition of the sugar
decreases the required boiling time from 30 minutes to
roughly 60 seconds (at least in the microwave oven), the
exact time depending on the substrate being used and
possibly other factors. The one real problem is that
the amounts of clay are given as parts, whereas the
amounts of other materials are given as grams. (This
may be an artifact of the translation.)

3. For testing purposes, it is not necessary to calcine
the pigment. Just mix it into the test glaze.

Reference:

Seger, H.


Collected Writings, Vol. 2 (translated into English, 1902), page 664


The Chemical Publishing Co., Easton PA

Last modified: Sat Oct 22 03:10:19 EDT 2011