What Painting Is: How to Think about Oil Painting ... - Victoria Vesna

3
The mouldy materia prima
IT IS POSSIBLE to grow a golden slug in a bath of acid. The
nineteenth-century alchemist Stephen Emmens describes the
method in his book Argentaurana: it begins with a few drops of
tannic acid, C 11H 10O 9, in a big bottle of water. 1 (In the
seventeenth century, alchemists would have gotten tannic acid
by sawing the galls off oak trees, drying them, pulverizing them,
and mixing the powder with water. Emmens probably got his
tannic acid from a chemical supplier.) The diluted liquid tastes
faintly astringent, like soured water left standing in a rainbarrel.
Into it the alchemist drops a solution of gold chloride.
The effect produced is magical. Threads and skeins of
amethyst grow and steal and creep through the liquid, and
gradually deepen into the most magnificent purple.
By stirring, the fluid becomes uniformly colored; and if a
quantity is prepared and kept for a considerable time, a
black substance makes its appearance in the form of a
shining slimy mass, which when lifted out on a glass rod
hangs pendant and looks remarkably like a slug. It is a
metal and is soluble in water and ammonia; but when
heated in the flame of a spirit lamp it assumes the aspect
and takes on the properties of ordinary gold.
A black slug, made of gold? The recipe seemed unlikely to several
modern chemists, and they tried to reproduce it. According to
their experiments, the slug is nothing but a pile of mould:
For our experiments we used one drop of a 1% gold
chloride solution prepared by dilution of a commercial 75%
HAuCl 4 3H 2O solution and 10 ml of a series of tannic acid