I’m with Mike C. I tried canned air on.. something I’d rather not say (NOT a harp!) and apparently held it at the wrong angle? I don’t know that I did.. but anyway, totally ruined the thing I was trying to take care of so lovingly. It’s a great idea! But I would pass on it with your beloved instrument.
I wonder about small-hosed vaccumes like I’ve seen certain mechanics with?
Canned air is made up mostly of fluorocarbons, which wouldn’t have much reactivity with metals to the best of my knowledge. There are plenty of metal parts in your computers and such – metal parts that would be much much more sensitive than the comparatively sturdy harp action. I wouldn’t worry about the metal bits.
I can’t say that I know what the varnish is made of, or how it would react, but I can say that the product is designed to be used in spurts. That is to say, not much of the gas would actually be touching the harp, and it dissipates rather quickly (otherwise it would be a health hazard).
The primary concern is temperature, and if the instructions are followed, there is no reason why the gas would be coming out much colder than room temperature.