Hi Ya'll:
Years ago an old HOUSE painter gave me a tip about storing paint. he said to me simply and directly. "Young man" Said He," do this and your painting will always be a joy". I asked him and this was his reply." Your little cans and bottles are good storage containers for sure" Now, I already knew that. His next comment I have taken to heart."Take your opened containers, Clean the inside of the lid carefully and then the top rim of the bottles and the paint groove in the tins." "Clean around those little Humbrol lids until they shine." Then make sure they are secured tightly, if you are going to store them for while".
Put them in a box and store them in a cool dry place always. You wil be able to keep them for years". Well, as you all know I was recently gifted the first edition of Tamiya's U.S.S.Missouri. Kit number 78008. So I needed my favorite deck color from Humbrol, Yup, that's right, Deck Bleached Teak. I don't remember the number and the label was missing that info. Old labels do get damaged for sure!
Anyway, by matching colors I found four unopened tins and one opened one. Imagine my surprise when I opened the oldest one( The used One) and the color, though settled and seperated did indeed mix back up and was just as fine and lump free as if it was new! That tin has to be at least twenty five years old! I bought a lot when Doing commissions years back. So, in closing Clean, Seal well and dark Places are the cure. Don't store paint in Sun, Heat , or Damp. Cool and Dark does the trick!!!
NOTE:
This apparently has worked as well, for the few Acrylics I bought back when they were ONLY craft paints(Dollhouses, and Stuff).