[Spock's face practically beams at the approval of the gift... he had been worried.]

You have Miss Fujiko to thank for that once again Sa-kai.... once I found out your musical ability, I set to work right away in anticipation of your arrival. [Spock did not tell Lupin that there was a small inscription in Vulcan on the neck of the instrument... it was difficult to see unless you were looking for it.]
However, the stain only managed to fully dry last night.