Posted 09 October 2004 - 08:57 AM
Dry them until they're dry. How long that takes depends on the temperature, humidity and level of air movement.
You can tell if they're dry by weighing them. Obviously, as the solvent evaporates, they will get lighter. Once they stop getting lighter, you know solvent has stopped evaporating, which probably means they're dry. For example, if you started with 100g of dry star comp, and formed it into stars, the mass may change something like this:
On the first day, you have the 100g of comp you started with, plus the 20g of solvent you used to form the stars. After a week the mass has stopped decreasing, suggesting that all the solvent has left the composition. They have also reached about the same mass as the dry comp you started with. They may weigh a little less due to some comp being left on your tooling, or a little more due to the addition of cores, if they were rolled (you could weigh these as well, to allow you to be more accurate).
There isn't really any need to weigh them for the first few days, as you know they won't be dry then. What you're interested in is finding out when the mass has stopped changing, and reached it's original level, so I'd just let them dry for a few days, then weigh them, weigh them the next day, and again, and if the mass remains fairly constant I'd presume them dry.
It is worth noting that if the weight were to decrease from the initial 120g, to say, 115g, and then stop, you know that something is wrong, since you only used 100g of comp. This is a sign that the stars are driven in, and the solvent is still there, but not evaporating. However, this is unlikely with 10mm tiger tail stars.
The final, and obvious test for dryness, once their mass has ceased changing, (or, having said that, just after a few days, without bothering to weigh them) is to actually test one. If it performs as it is supposed to, you can seal the rest of the batch up in an airtight container (I like cheap Tupperware boxes). Don't use glass jars for storing mixtures in, if any were to get caught in the thread and ignite while you were screwing the lid on, well you can imagine...
Finally, since it's getting to that time of year where stuff is reluctant to dry outside, I have been looking for a way to build a cheap drying cupboard. What I am using is big, lidded plastic bucket with a jar of anhydrous magnesium sulphate (baked Epsom salts) in the bottom, and a stack of shelves for stars, pasted shells etc above. An old refrigerator would be ideal, since it's airtight, easy to access and already has the shelves in, but I didn?t have one. So far, it's worked well, and it's cheap to construct and run, and very safe, as it will work anywhere.