John Shade's winterscapes were engendered at a time when trees were loaded with leaves and the waxwings berrypicked. As C.Kinbote notes: "How persistently our poet evokes images of winter in the beginning of a poem which he started composing on a balmy summer night! The mechanism of the associations is easy to make out (glass leading to crystal and crystal to ice) but the prompter behind it retains his incognito. One is too modest to suppose that the fact that the poet and his future commentator first met on a winter day somehow impinges here on the actual season." (note to lines 34-35, on "Stilettos of a frozen stillicide." )

Shade once mentioned "a crystal land"(line 12) that Kinbote immediately associated to Zembla before the coup, when those "who knew too much, scientists, writers, mathematicians, crystalographers* and so forth, were no better than kings or priests..." 

His inclusion of "crystalographers" is intriguing. Before that, Kinbote had made two other alusions to crystal in his foreword: "Knowing Shade’s combinational turn of mind and subtle sense of harmonic balance, I cannot imagine that he intended to deform the faces of his crystal by meddling with its predictable growth." and his witnessing of Shade's observation about a snowflake that fell on his wrist watch:. " Crystal to crystal." In his note to line 426, Kinbote comments on Shade's verse making a reference to Robert Frost: "The line displays one of those combinations of pun and metaphor at which our poet excels. In the temperature charts of poetry high is low, and low high, so that the degree at which perfect crystallization occurs is above that of tepid facility" and he closes the note with a dismissive: "With all his excellent gifts, John Shade could never make his snowflakes settle that way".

Everything in "Pale Fire" (a title that is also suggestive of a diamond's reflectiveness) that relates to the process of crystallization is associated to water, not to stone nor salts. Therefore, it's only through a wild leap of imagination that I can include, among the hypothetical allusions, a reference to Stendhal's theories about "crystallization." (related to salts).

The idea is not as far-fetched as it may seem at first. Nabokov would have read the great French stylist. Besides, I remember that either in "Lectures on English Literature," or in "Strog Opinions," Nabokov observes how ordinary looking women, such as Proust's Emma, even HH's Lolita, are seen through the special lenses of amorous infatuation - and this Stendhal's famous theme (btw: Shade's neurotic symptoms are reminiscent of Stendhal's own while he was visiting Florence)**.

Cf. Wikipedia, the free encyclopedia: "Crystallization is a concept, developed in 1822 by the French writer Stendhal, which describes the process, or mental metamorphosis, in which unattractive characteristics of a new love are transformed into perceptual diamonds of shimmering beauty; according to a quotation by Stendhal: What I call 'crystallization' is the operation of the mind that draws from all that presents itself the discovery that the loved object has some new perfections.
In the summer of 1818 Stendhal took a recreational trip to the salt mines of Hallein near Salzburg with his friend and associate Madame Gherardi. Here they discovered the phenomenon of salt “crystallization” and used it as a metaphor for human relationships. [   ]Thus, according to Stendhal, the moment one begins to take interest in a person, one no longer sees him or her as they really are, but as it suits one to see them. According to this metaphor, one sees flattering illusions created by a nascent interest; illusions analogous to pretty diamonds hiding a leafless branch of hornbeam, perceived only by the eyes of the one falling in love.***
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* - "crystallographers", I suppose (it is spelled with one "l" on p.546 in the edition of The Library of America (Nabokov Novels 1955-1962)    If with one "l" then, perhaps, "crystallization" should obey to the same criterion?

** - wikipedia: Stendhal syndrome: In 1817 Stendhal reportedly was overcome by the cultural richness of Florence he encountered when he first visited the Tuscan city. As he described in his book Naples and Florence: A Journey from Milan to Reggio: "As I emerged from the porch of Santa Croce, I was seized with a fierce palpitation of the heart (that same symptom which, in Berlin, is referred to as an attack of the nerves); the well-spring of life was dried up within me, and I walked in constant fear of falling to the ground." The condition was diagnosed and named in 1979 by Italian psychiatrist Dr. Graziella Magherini, who had noticed similar psychosomatic conditions (racing heart beat, nausea anddizziness) amongst first-time visitors to the city.
In homage to Stendhal, Trenitalia named their overnight train service from Paris to Venice the Stendhal Express.

***-  Applications: Psychologist Dorothy Tennov describes the process as a transformation in which the loved one’s characteristics are crystallized via mental events and neurological reconfigurations such that attractive characteristics are exaggerated and unattractive characteristics are given little or no attention. She uses this basis for her description of a "limerent object", related to the concept of limerence

References: De l'amour, Paris, 1822 ;  Stendhal (1822). On Love. New York: Penguin Books. ISBN 0-14-044307-X. ;  Tennov, Dorothy (1979). Love and Limerence. Maryland: Scarborough House. ISBN 0-8128-2328-. .