I have a bottle of unopen, factory sealed Tetenal Gold Toner which has been standing in a warm cupboard for the best part of 2 years, possibly a little longer. I believe I'm right in saying that, basically, it won't go 'off'. But I wonder whether after standing that long in might 'settle out' and form a crust in the bottom which might not break to become a uniform liquid again after decent shaking.
Observations please.....