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

26 WHAT PAINTING IS
each liquid have its own gas? These are all unanswerable
questions without knowledge of modern chemistry, and so they
correspond roughly to what the alchemists had to work with.
There were other problems as well. Since the alchemists had no
graduated thermometers, they also had no way to quantify heat
and cold. Instead of measuring temperatures, they classified
“grades” or “species” of fire. Each species had its own essential
properties. The medieval alchemist Artephius specifies three
fires: the fire of the lamp, “which is continuous, humid,
vaporous, and spiritous”; the fire of ashes (ignis cinerum), which
makes a “sweet and gentle heat”; and the natural fire of water,
“which is also called the fire against nature, because it is
water.” 29 Like many unscientific insights, this one has what we
now can only call a poetic truth. Water does have its heat, and so
it is like the heat of flame, but less strong. The
seventeenthcentury alchemist Johann Daniel Mylius said there
are four heats: that of the human body, of sunshine in June, of
calcining fire, and of fusion (he means chemical fusion, not
nuclear fusion). Other authors specify the heat of a manure heap,
or of a brooding hen, or of a virgin’s breasts. (That is the mildest
heat, the one closest to coldness.) Usually the hottest species of
fire was “wheel fire,” a heat so intense that the flames would
encircle the crucible. The lack of thermometers was the despair of
experimentally-minded alchemists who wanted to tell their
friends how to make some special substance, because there was
no dependable way to give the recipe. It is no wonder the
Rosicrucians called fire “the great indescribable spirit,
inexplorable in eternity.” 30
If it was to be possible to come even close to repeating an
experiment, the alchemists needed to describe differences in
heat, color, and time without thermometers, spectrographs, or
accurate clocks. In this vein Marius, a medieval metallurgist, tries
to define the major metals as exactly as he can:
Iron is made from dense quicksilver mixed with sulfur of a
color halfway between red and white, and it is cooked for a
long time, even longer than copper, by a moderate heat….
Copper contains a small amount of redness, so if iron lies
undisturbed a long time, it becomes rusty and takes on a
reddish color.