Lacquer cracks

[Stray Feathers]

In May of 2021 I finished my first three tenor ukuleles. One was an add-on because I found I could get a uke back and sides out of some scrap Wenge from a furniture maker. This one was gifted to one of my wife's daughters. This weekend she showed me cracks that had developed in the finish (Mohawk lacquer). She says they just appeared recently. She can't remember any time when the uke might have been exposed to heat, but she spent part of last winter with her sister in Saskatoon (cold and dry). There is also a long closeable crack in the Wenge back I might try to close with CA and Gluboost. It's a bit alarming to see this, but none of my other instruments show any similar signs, including the other two ukes built at the same time (Bitter Cherry and Western Redcedar). I have seen a video in which Mamie Minch uses lacquer retarder to close or fill old finish cracks. Any thoughts on this appreciated. Bruce W.

[RLR33]

Following this. I have 2 dreds with the same problem.

[TEETERFAN]

Did they undergo a quick temperature change? Especially “cold” to “warm”?

[RLR33]

Not to highjack Stray Feathers thread, But I live in south Fl it doesnt get "cold" here.

[Stray Feathers]

The owner moved from Vancouver Island to Saskatoon in winter. It's possible that the ukulele was left in her vehicle overnight along the way, so pretty cold. The more I think about it the more I think it must be something like this, since this is the only one of my instruments to crack like this.

[Skarsaune]

Cracks like that are a desirable 'feature' for the relic'd crowd.
You can artificially induce them with a variety of heat/cold cycles & techniques.

They are also pretty normal for vintage guitars. I've got a ~30 year old Gibson that has a few.
I look at them kinda like grey hair - well earned marks of distinction. :-)

[BlindBo]

If you want to remove them, I have used a 50/50 lacquer thinner/retarder mixture appilied right over the crack using a toothpick. It takes a lot of patience to get it to blend in. Normally takes level sanding that area and going through the whole finishing process to make it disappear. From the pictures, you may end up having to refinish the whole top.
Like the post above, I have several old guitars with lots of checking and kind of like the look.
Good luck.

[Stray Feathers]

Thanks for the input. Because this instrument is only about three years old, it doesn't seem right for it to already have "vintage" cracks. I feel a bit responsible for it even though I am more and more thinking it was a temperature or humidity change that triggered it. Blindbo, I will try some retarder on it. I tried that on some newer finish blemishes with some success, having learned it from this video featuring Mamie Minch (her dad was an active member of this forum until his untimely passing):

https://www.stewmac.com/video-and-ideas ... ar-finish/

And I think you are probably right that this will ultimately involve a more overall re-sanding and buffing. There is also a long, fine crack (perhaps two) on the Wenge back to think about - probably before rather than after the lacquer cracks. Bruce W.

[TEETERFAN]

When an instrument is cooled to a low temperature for several hours, it slowly shrinks uniformly. If it is exposed to warmer air abruptly, the smooth exterior/outside warms slower than the porous, unfinished interior. The rougher, open surface inside exchanges the heat faster, expands quicker, and cracks can result. That’s why several builders think that some type of interior finish makes sense.