Moon-letters

Moon-letters were a method of writing invented by the Dwarves. Moon-letters were ordinary Runes, but written in such a way that they could only be read when the light of the moon shone behind the writing. Some moon-letters could be read by any moonlight, but it was possible to make the writing even more secret. More sophisticated moon-letters could only be read by the light of the same shape of moon, or at the same time of year, as when they were written.

Moon-letters were written with silver pens.^[1] The substance Ithildin, made from mithril, reflected only starlight and moonlight,^[2] and it seems likely that ithildin, or something very similar, was used by the Dwarves to write their moon-letters.

An example of moon-letters was found by Elrond on Thrór's Map of the Lonely Mountain and surrounding areas that Gandalf had given Thorin in T.A. 2941.^[3] The moon letters were of the more cunning type had been written on a Midsummer's eve under a crescent moon. They said:

"Stand by the grey stone when the thrush knocks and the setting sun with the last light of Durin's Day will shine upon the key-hole."^[1]

References

1. ↑ ^{1.0 1.1} J.R.R. Tolkien, The Hobbit, "A Short Rest"
2. ↑ J.R.R. Tolkien, The Lord of the Rings, The Fellowship of the Ring, "A Journey in the Dark"
3. ↑ J.R.R. Tolkien, The Lord of the Rings, Appendix B, "The Third Age"