Google provides quite a few links (if you search for “glass tambourines” instead of “crystal”).
However, contrary to the recent popular opinion, not everything is to be interpreted, to be determined by the judgment of certain masters of the hidden meaning.
Lorca didn’t exactly mean anything – instead, he composed an image that provides a reader/listener with associations and feelings. See the essay The Duende of Lorca’s Diván del Tamarit by E.A. Melino:
Lorca’s images are not symbols to be decoded or metaphors whose
parallels can be puzzled out. Hecho poético doesn’t live in the head.
Like flamenco music, it is experienced in the body, particularly the
belly and hips. The question is not “What does the poem mean?” but
“What do you feel?”
This is why explanations deal more with the associations of some kind. Here’s an essay Lorca, poet of Granada by Lawrence Bohme:
As they ascend, the light from "tiny tin lamps" - of the sort gypsy
craftsmen make – flickers on the village houses, and "a thousand
tambourines" – an instrument the gypsies play – "of glass" (perhaps
symbolising the stars and the early morning frost) "wound the dawn"...
Or consider A Generation of Spanish Poets 1920-1936 by C. B. Morris:
he associated tambourines, glass and the dawn to record an original
vision of dew glittering at daybreak
By linking and interlocking the five senses in his ballads, Lorca
brought the reader's own senses into play, involved him in a complex
of new sensations that are as strange to experience as they were to
The last thing. What about Lorca’s own statements? Did he say that he didn’t mean anything at all about this poem and about exactly the same verse? Would it be a strange coincidence?
Metaphor, Lorca insisted, must give way to the hecho poético the
"poetic event"-a phenomenon at once illogical and incomprehensible, as
miraculous as “rain from the stars.” In a subsequent version of his
lecture, he cited a passage from one of his own Gypsy poems, the
"Sleepwalking Ballad," as an example of an hecho poético. "If you ask
me why I wrote 'A thousand glass tambourines / were wounding the
dawn,' I will tell you that I saw them, in the hands of angels and
trees, but I won't be able to say more than that, much less explain
their meaning. And that's how it should be."
He regarded the hecho poético as one of several means of reaching the
purest plane of poetry, the "poetry of escape.” The surrealists sought
to achieve "escape" through dreams and the unconscious, a method Lorca
found pure but unclear. “We Latins want sharp profiles and visible
mystery. Form and sensuality.” As much as he admired Dalí and
respected the artist's views on surrealism, Lorca refused to subscribe
to any such movement.
(From Lorca - a Dream of Life by Leslie Stainton, boldface mine)