White stains on the finishing issue

I don’t know what caused it that depends on the finish.

Strippers over veneer can be risky I would start by sanding it with something like 220. Don’t go near it with a sander do it by hand.

You might be able to lightly sand and apply a coat of poly. Worth a try.

-- Everything is a prototype thats why its one of a kind!!

Looks like a water-based polyacrylic applied with a spray gun. The directions only mention using a brush and not over-brushing.

-- Phil Allin - There are mountain climbers and people who talk about climbing mountains. The climbers have "selfies" at the summit!

Welcome to LumberJocks!

That looks like lacquer blush? Lacquer turns milky when moisture in trapped in the coating.

Before I would start sanding, I would test in hidden spot for lacquer finish?
https://www.woodmagazine.com/materials-guide/finishes/what-finish-is-that-anyway

While it is rare to happen indoors, fully dried lacquer can turn milky if water sits on surface long enough, or bottom was not sealed and moisture is sweating up due high heat and trapped moisture in wood.

Lacquer does not cure, and can melt or reflow the coating with proper lacquer thinner. BORG lacquer thinner won’t work well, need real lacquer thinner from industrial coatings supplier.

When Blush happens during finishing, simply add some retarder, and spray a light coat to lacquer to magically release the moisture. Or can spray straight lacquer thinner with retarder to keep same film thickness. Higher local humidity, the more retarder solvent needed to slow lacquer thinner evaporation and let moisture escape before the lacquer finish dries.

Mohawk sells a No Blush in spray cans for repairing lacquer blush on finished items.
https://www.mohawk-finishing.com/products/wood-touch-up-repair/aerosols/no-blush-plus-retarder/
Find a ‘dry’ day with less than 50% moisture, and mist a light even coat on top. Be careful not to pool the ‘No Blush’ as it will create lines at edges of puddles. Follow mfg instructions and it will remove lacquer blush.

Best Luck.

-- If it wasn't for bad luck, I wouldn't have no luck at all, - Albert King - Born Under a Bad Sign released 1967

Thank you for your replies.

Since I live in Dubrovnik, Croatia (a.k.a. King’s Landing from the Game of Thrones), there are no specialized shops where I could buy something as you mentioned. Anyway, maybe I will try to remove old finisih one day but at the moment my father installed dark brown glass to cover the stains and it looks fine.

Since I live in Dubrovnik, Croatia (a.k.a. King s Landing from the Game of Thrones)....
- arhitekt

Croatia location changes everything.

Suggest you look for AkzoNobel wood coatings distributor in your area.
AkzoNobel has massive number of brands, many selling the same finish materials in can, but different brand sname in different countries. Sikkens Wood Coatings products are common in many parts of EU.
www.sikkens-wood-coatings.com

Another tip: Lacquer no-blush solvent is not a magic potion. It is simple (to chemist) blend of solvents. Lacquer paints were extremely popular in mid 1900’s for automotive finishing. Another potential source of no-blush solvent blend would be automotive finish supplier like Axalta distributor. They have several country specific brands of auto paint, so usually best to call or visit.

If you can’t find Lacquer no—blush product, can always buy raw solvents from Automotive paint store and make you own using Mohawk SDS as guide.
When I consulted for several EU Electronics mfg, we often had to buy raw solvents from Automotive paint suppliers as the industrial demand was too low for our special blends for anyone to sell it locally, and US shipping where it was commonly used was too expensive.

Best Luck.

-- If it wasn't for bad luck, I wouldn't have no luck at all, - Albert King - Born Under a Bad Sign released 1967

I agree with the CaptK…it looks like lacquer blush. Test a hidden spot to determine if it is lacquer. If it is a light spray coat of lacquer thinner could solve the issue by softening the finish enough to allow the moisture to escape, then it will dry clear.

-- Sam Hamory - The project is never finished until its "Finished"!

Another name to search for is “blush eraser” which is a spray that will reflow lacquer and allow trapped moisture to escape. Mohawk or Behlen are brands that offer this product. Perhaps a local brand will have something similar. Good luck.

-- I love the smell of sawdust in the morning.