The symbolism of alchemy runs through Blake's writings and will be apparent to those who seek it out. The basic symbolism of alchemy is of transformation. Although the original object was to produce gold from base metals, the discipline was later spiritualized to that of becoming transformed oneself by the processes which were developed in the laboratory for transmuting elements.
Click on this picture from MHH Plate 14 to enlarge an image of transformation by fire.
There is a chapter on Alchemical Symbolism in Milton O Percival's book, William Blake's Circle of Destiny. William Blake's acquaintance with alchemy was primarily through Paracelsus and Boehme whom he acknowledges as influential in his thinking. Among the prominent patterns of thought in alchemy which are noticed in Blake are:
>The four elements - air, water, fire and earth,
>The original state is unified,
>The centrality of reunifying male and female,
>Fire as the liberating and regenerating agent,
>That all things are alive and sentient,
>Achieving life through death,
>Transformation of body into soul.
In my post on Angel & Devil, in the passage I quoted, the Angel at the point of transformation undergoes mutations of color which are the primary indication that the crisis has been reached. Color changes were outward manifestations that hidden change were taking place in the alchemical processes.
MHH plate 22
"The Angel hearing this became almost blue but mastering
himself he grew yellow, & at last white pink & smiling, and then
Los' work at his furnaces is the work of the alchemist. Here is a quote from page 212 of Circle of Destiny:
"Los handles the purification of the contraries in the furnaces in accordance with alchemical tradition. As in alchemy the imperfect triple body (salt, sulphur, and mercury) has to be broken, and the masculine sulphur and the feminine mercury freed for purification in the fire, that they may be united in the one only essence, so must sinful man, his doubting head and cruel heart selfishly combined into a mortal body, be subjected to trial by fire, that his divided selves may be reunited in the one man Christ. But, though man himself is metaphorically the sum of all that is in the furnaces, the forms (or bodies) which Los continually breaks down should be thought of as forms of government, of religion, of what you will - forms constructed by a crafty head or a cruel heart. The intellectual life (the theory, the dogma) of these forms must be broken down in order that the chastened emotions may be set free for a new fixation under the guidance of a liberated intelligence. In alchemical parlance, two must be drawn out of the three and separately purged before the transforming union can take place."
Blake writes of a world in need of renewal and regeneration. He uses the symbols of alchemy in presenting his complex myth of breaking down the destructive systems and opening the way to transformation to the new age.
Jerusalem, Plate 78, (E 233)
"Los with his mace of iron
Walks round: loud his threats, loud his blows fall
On the rocky Spectres, as the Potter breaks the potsherds;
Dashing in pieces Self-righteousnesses: driving them from Albions
Cliffs: dividing them into Male & Female forms in his Furnaces
And on his Anvils: lest they destroy the Feminine Affections
They are broken. Loud howl the Spectres in his iron Furnace
While Los laments at his dire labours, viewing Jerusalem,
Sitting before his Furnaces clothed in sackcloth of hair;"