Do bottle paints get old????

Most of my modeling supplies were purchased in the early 90's. I have mostly Tamiya and Gunze paints. Some of these were never opened and are thin but some are kinda thick. I tried thinning it with alcohol but am not sure if they are still good.

On one particular paint a Gunze tire black I tried to thin for pannel lines and other flat black areas I had bad brush streaks when dried. Was I supposed to use water instead of alcohol for a thinner?

Does anyone have a idea what the shelf life of a paint would be. I would think as long as the thing isn't dried solid then it should be O.K..

Any suggestions? Thanks!

For panel lines you should use enamels on top of lacquers for ease of buffing and that enamels don't set into lacquers.

If you have a very large collection of those old paints then I think most of them can be used if you shake them vigorously and leave the bottles in hot water for a few minutes to get the paint flowing beter.