I must add that it does depend on the colour. Some form a thick layer of pigment sediment in the bottom of the tin that you have to stab to pieces with a cocktail stick before you can even begin to stir, while others that are just as old can be stirred right away and be usable within two minutes instead of ten or more.

All in all, I don't use Humbrol paints much anymore, but still enough that when I come across old tins of it (which means from before the "Super Enamel" range they introduced about 25 years ago), I always check if there are any I can use. At a model show last February, for example, I purchased the ones you can see in this photo:

[ATTACH=full]133093[/ATTACH]

All of them are old to ancient (1990s down to '70s production, going by the tins) but I have no reservations about using them still  However, only sparingly: for washes, drybrushing, etc. I don't paint whole models with them anymore.