I've made a few batches of hard crack candy, but so far every batch i've made has come out stickier than I'd like. by too sticky, i mean that the candies will stick to the parchment paper i store them in so hard that the two become inseparable. this happens even in the freezer.   So far I've tried   letting the temperature go up a little higher on the candy thermometer (310-320) adding powdered sugar after the candies have cooled down   as experiments but to no avail. what can people recommend? is there an additive i could add to the mix?  
I have the answer to this and as someone above said, it is to do with humidity. I make toffee apples to sell and have found out by trial and error that  you have to make sure they are definitely heated to 150°C so that the mixture goes immediately solid when dropped in cold water and Wrap them in cellophane the minute they are cool enough, so probably within 5 minutes of cooking. They get sticky quickly if left in contact with the air. If you wrap them they will remain hard like glass and not tacky.  