I would like to suggest an interpretation of a curious phrase which appears on Plate 65 of Jerusalem.
They vote the death of Luvah & they nail’d him to Albion’s Tree in Bath,Damon identifies “poisonous blue” as woad.1↤ 1 S. Foster Damon, William Blake: His Philosophy and Symbols (1924; rpt. New York: Peter Smith, 1947), p. 459. And given the general context, a Druid sacrificial rite, it does seem likely that Blake was thinking of the dye with which ancient Britons colored their skin. Yet there is nothing particularly poisonous in the chemical makeup of woad. Therefore I suspect that Blake may also have had in mind another coloring substance—the pigment known as Prussian blue.
They stain’d him with poisonous blue, they inwove him in cruel roots
To die a death of Six thousand years bound round with vegetation. (J 65:8-10, K 699)
Prussian blue was first produced in Berlin in 1704 and by the end of the century had come into wide use among artists—Blake included.2↤ 2 Sir Geoffrey Keynes and Edwin Wolf 2nd, William Blake’s Illuminated Books: A Census (New York: Grolier Club, 1953), pp. 44. One instance of Blake’s use of the color is mentioned. In 1782, the new pigment aroused the curiosity of the Swedish[e] begin page 89 | chemist, Karl Wilhelm Scheele, and he performed a series of experiments attempting to analyze the “coloring principle” in Prussian blue.3↤ 3 His account of the experiments is included in The Chemical Essays of Charles-William Scheele, trans. Thomas Beddoes (London: John Murray, 1786). Scheele was successful in isolating the chemical, and four years later the French Encyclopédie gave it the name “l’acide prussique.”4↤ 4 J. R. Partington, A History of Chemistry, III (London: Macmillan, 1962), 527. Prussic acid is today more generally known as hydrocyanic acid or hydrogen cyanide, and it is recognized as one of the most poisonous substances in existence. Scheele himself was apparently not aware of the dangerous qualities of the acid he had discovered: it was not until 1803 that its highly poisonous character was fully understood.5↤ 5 Partington, III, 234. In 1803, the poison derived from laurel leaves was identified as prussic acid. Was it coincidental that in this year (probably) Blake wrote: “The Strongest Poison ever known / Came from Caesar’s Laurel Crown”? (K 433) Or had he read somewhere an account of the discovery? Since then the chemical has had an inglorious history: the Zyklon-B used at Auschwitz and the gas released in execution chambers in this country were both forms of hydrocyanic acid.
What was Blake’s point in alluding to Prussian blue in this passage? David Erdman suggests that Plate 65 was revised at about the time of Napoleon’s Hundred Days.6↤ 6 Blake, Prophet Against Empire, 2nd ed., rev. (Princeton: Princeton Univ. Press, 1969), p. 466n. In the Belgian campaign—that final assault by the sons of Albion against Luvah—England’s chief ally was Prussia. It was the arrival of Prussian troops under Blücher that determined the outcome of the battle at Waterloo. In describing the sacrificial death of Luvah, Blake saw the appropriateness of identifying the blue dye of the Druids with the poison-based color named for Prussia.