Aged Amber Lacquer
The perfect "toner"
Years ago I discovered a can of old nitrocellulose lacquer hidden way back behind a lot of old junk in the back room. This can was so old that the bottom had begun to rust just a little inside. The lacquer inside was seriously discolored, but I really liked the color.
I was a little nervous about using this damaged lacquer on a valuable guitar top, so I used it on some shelving instead. I called the lacquer manufacturer and asked about the stuff. He said that the rust discoloration would probably not affect either the working or service characteristics of nitrocellulose lacquer.
Then I had a bright (for me) idea. I asked him about ultraviolet color damage. He reassured me that there would be no damage to the lacquer if I let it discolor naturally before using it.
Now, I keep some of my lacquer in clear bottles right on top of my garage roof.
It's a flat roof, so the bottles won't fall off! The bottle on the right has been up there for almost two years. It's really getting dark.
When I'm finishing a vintage guitar top, or doing a bit of touchup on an old lacquer finish, I can match the amber tone with real precision, because I have the real thing!
By the way, the rust damaged lacquer I used on the shelving is still fine after about 15 years.