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Prussian Green

The euonymous Boyle: among his many unsuccesses were more than a few spectacular discoveries. Mezzotint of Robert Boyle after van der Vaart (1727), © The Trustees of the British Museum.

My reading these days includes a lot of Robert Boyle’s two essays on failure: “Of the Unsuccessfulness of Experiments,” and “Of Unsucceeding Experiments.”  They are similar in title, but not so in matter; Boyle has lots of examples of chemical things not going his way.  But that seems about right to me.  There is a lot of repetition in chemistry—I mean doing things again and again, since chemistry is about learning through repetition.  And among those repetitions, there’s a lot of unsucceeding.  In fact, as Boyle himself notes, there’s many more ways to unsucceed than succeed: and if there’s enough discussion of a successful experiment to fill one essay, there’s more than enough failure to fill many, many more.  Even the categories of unsuccess are enough to fill two.

Prussian Brown. This toxic mess smells as foul as it looks.

I have been plenty unsuccessful in trying to replicate the eighteenth-century color called Prussian Green, a precursor reagent for the better-known Prussian Blue.  After six or seven batches, I’ve got it mostly sorted out—of which more below—but the unsuccesses are the important thing, here.  For Prussians Green and Blue were themselves the product of a different kind of unsuccess: one Boyle doesn’t mention, though he must have known about it.  Prussian Blue, and its green precursor, were the first true synthetic pigments.  Others, like the botanical lakes, aren’t synthetic, because they simply liberate a dye molecule from plant-matter and attach it to a substrate.  A few pigments, like verditer, generate new color molecules from bare chemical reagents; but because verditer was known, even then, to be only an artificial form of the mineral azurite, it hardly counts as a true synthetic pigment.  Prussian Green and Prussian Blue are different; the whole process of synthesis is aimed specifically at creating the pigments, and in this sense, they are the first of their kind: the first synthetic colors, the first time, as far as we know, that someone consciously won a new pigment from the universe.

But the discovery of Prussian Green appears to have been an unsuccess of that other sort, the type not named by Boyle.  Boyle names unsuccess by virtue of materials which have been adulterated—or not adulterated enough; by dint of the want of skill in a technician; by failures in recording or correctly understanding another natural philosopher’s technical vocabulary; by want of attention to details that appear insignificant—or don’t appear at all—but nevertheless effect the result; and so on.  I chalked up instances of all of these just in repeatedly unsucceeding to make rose pink, which I now know is a relatively simple color to make.  What Boyle doesn’t discuss is the unsuccess which is productive of something else, which, in fact, almost all unsuccess is.  An artisan cannot help learning by failing—and sometimes they learn something astonishing.  That last category: that’s the case of Prussian Green.

Johann Conrad Dippel, occult alchemist. Image © The Trustees of the British Museum

The standard account of its discovery begins with Johann Dippel, a physician and occult chemist who may have provided a model for the brilliant and obsessive doctor of Mary Shelley’s novel Frankenstein.  Sometime around the turn of the 18th century, he had set up a laboratory in Berlin; he was chasing an elixir of life that later generations have called “Dippel’s Oil.”  The work involved combining animal blood—the life-bearing reagent—with potash, a potassium salt leached from wood ash.  Sharing space in the same pungent laboratory was Johann Diesbach.  Diesbach was a Swiss color chemist laboring to discover the trade secrets of a red pigment called Florentine lake.  He had prepared nearly everything he needed in his latest batch of pigment when he discovered he was short of potash.  In what must have been a common exchange, Diesbach borrowed a quantity from Dippel, neither realizing that it had already been contaminated with calcined animal blood.  Combining that contaminated mixture with the prior lixivium immediately produced a sludgy green precipitate; washing with spirit of salt—our hydrochloric acid—transformed it into a blue one.

When an acid meets a base: instant chemistry.

As far as we know, Diesbach never did figure out that Florentine lake.  His fame is different, and more magnificent; he brought a new pigment into the world, indeed, a new kind of pigment.  It’s a good story for chemistry.  Chemistry is all about novelty.  It repeatedly takes substances of two sorts—an acid and a base, for instance—to produce something new.  Just so, in Dippel and Diesbach’s shared lab, two different kinds of chemistry combine to introduce a new pigment into the world.  Something has happened, in the space between expectation and experiment, what Francis Bacon called a “knowledge of art.”  The advance was made not because the first principles of the color or its chemistry were understood; these are still somewhat a matter of rules of thumb—I mean why it is that the Prussian green molecule looks green, rather than some other color.  Rather, the invention was achieved by a skillful artisan who happened on something interesting while looking for something else.

Berthold Schwartz, about to wake the upstairs neighbors. André Thévet “Inventeur de l’Artillerie,” © The Trustees of the British Museum.

Happening on something while looking for something else—a green while seeking a red—is what Horace Walpole in 1754 would call “serendipity.”  This names the magic that happens when accident meets sagacity, when an unexpected event occurs in the presence of a person who can interpret it in a useful way.  It joins, by popular account, other such inventions, like the discovery (Bacon says) of gunpowder, owing to a monk accidentally mixing the right reagents over the stove and shooting the pot-lid into the room upstairs.  Now, to be clear, this is not how gunpowder was invented.  But Bacon’s account, which is akin to an etiological myth, explains the origins of a chemical discovery as a variety of cookery gone right in the wrong way.  For it to occur, there must be someone attempting something, in position to recognize the value of the wrong result—like a color-man synthesizing the wrong color.  So: Diesbach’s blue became Prussian Blue because he recognized its value.  Contrariwise, Dippel’s thick, resinous oil would only years later be marketed as an insect and animal repellant, an application the elixir-seeking alchemist never seems to have pondered.

Prussian Green, an unsuccess of the right sort. Photo for the Motley Emblem.

The next post will discuss the production of a batch of Prussian blue—including the construction and installation of a new piece of equipment in the motley lab.  But I wanted to share, here, a different serendipitous find, which can help shed light on the probable order of discovery of Prussians Blue and Green.  My first successful batch of Prussian Green did not look promising when it emerged from the filtration process.  Following the old chemist’s rule never to throw anything out until a process is complete, I set the yellow-green mud aside.  Two weeks of drying and mellowing on the gentle heat of the radiator, however, transformed it into a deep, foresty emerald pigment—the true hue of Prussian Green.  This, then, suggests to me something curious about the history of these colors, a mild paradox of discovery.  I suspect, that is, that Diesbach discovered Prussian Blue before its precursor, washing the muddy precipitate into Prussian Blue, only later to discover that that precursor precipitate matured into a useful pigment of its own.

More to follow, in Prussian Blue (forthcoming).