The Isle of Glass is the first novel in The Hound and the Falcon trilogy by Judith Tarr, published in 1985.
The Isle of Glass is a novel in which the elven hero, Alf, tries to prevent civil war and then begins a pilgrimage to Jerusalem.
[1] Dave Langford reviewed The Isle of Glass for White Dwarf #80, and stated that "Tarr can actually write.
Her spare prose and dialogue give a period flavour without the dread excesses of gadzookery.
Moreover, she's clearly a member of the Black Lords Anonymous and the Society for the Abolition of Quest Clichés.