One of my customers asked me to post this for everyone. He is a very nice gentleman and a good mandolin player and very fussy about his equipment. I guess that is why he got into the mess he did .
His mandolin was getting a bit funky under the strings near the bridge. He wanted to clean it and saw a can of air he used on his computer keyboard. He thought that would be an easy way to blow away the dust and skin cells from the top of his instrument. When he called he said he did that. He asked if I knew what happened next. I replied yes I do. It cracked the finish. He went on to explain that it indeed did crack the finish.
Compressed air in a can has chemicals in it that will crack the finish on your varnish or lacquer mandolins. It is one of many things used in a distressing process to accomplish certain cracking patterns. If you spray anything on your instrument you risk destroying the finish on your mandolin.
In this case, we were able to repair the finish to as good as new without having to redo the finish. The cracks are now gone, but it is not a DIY project by any means. Even then, we would not guarantee we could repair the finish. It turned out we could, but it was not a very inexpensive process. It was certainly more expensive than properly cleaning the instrument. He will have his mandolin back in a few days in new condition. However, this is one repair that we hope does not have to be repeated by anyone.
If you want a "distressed" mandolin, let a professional do it. While this is a way to crack a finish, it is not the only one and not always the best. Just remember to be careful about anything you put on your instrument. There are many things you would not think about that can ruin your finish. When in doubt, ask someone who would know and ask if they would do it to their instrument. In the end, if there is a question about whether it is a good idea, it usually is not.
There, I've done my duty for my friend and customer. We both hope you fare better than he and not do the same. And, remember, friends don't let friends play banjo! .