Posted 08 December 2012 - 12:43 PM
It really is all about practice and technique!
I'll address your points slightly randomly, as that's how my brain works ;)
Tempering cocoa butter is so ridiculously easy. I usually work with colours in 50-75g batches. I put the cocoa butter in a small (1 cup) plastic measuring cup and melt it to 45C (I have a dehydrator, so I just put it in there the night before I plan to work). Then take it out and stir it until it reaches 31-32C and it's tempered and ready to use. This will only take 5 minutes or so as the volume you're using is so small. Downside is, you have to work fast once it's ready, unless you have it kept warm. When you're finished, either leave it in the container to solidify, or pour it out in a thin layer over some clingwrap or nonstick baking paper, then store in ziplock bags (I do the latter). A side point: be so careful heating your cocoa butter in the microwave, it is incredibly easy to overheat and cause it to burn.
Chocolate will thicken naturally, as you've mentioned, even when held at the working temperature. This thickening is a multiplication of the beta crystals that are the "good" crystals that cause your chocolate to contract away from the mold. By adding pure cocoa butter, you do increase the fluidity however, you do increase the number of beta crystals that will end up being formed too! You can regularly zap it with a heat gun or hair drier, just a few seconds, to remelt the crystals that are forming at the cooler surface of the chocolate. If you're getting your chocolate thickening too much between adding it to the mold and scraping it clean, you've got far too many beta crystals in there - it's overcrystallised. You only need 1-2% of the liquid chocolate to be in the beta crystal state at working temperature for the chocolate to be "in temper". So it's easy to overcrystallise, too! Don't stress out about watching that thermometer though - heat the chocolate for a few seconds with a heat gun / hair drier, take a test. Rely on the test, not the thermometer - in the more advanced classes I've attended, the teacher doesn't allow the students to use a thermometer, it's all done by touch and test. Practice makes perfect!
Work one mold at a time. Don't fill 6 molds and scrape them after the sixth. Of course the chocolate will be thickening, if you do that (and I realise you never said you DID do that ;)). Always work clean - if you've got chocolate on your scraper, use a spatula or another scraper to clean it off. I hold the mold over the bowl, scrape the mold, wipe the scraper over the side of the bowl to get the bulk of the chocolate back into the bowl, then rescrape the top and then the sides, cleaning the scraper back into the bowl after every stroke.
Scraping the cooling chocolate back into your bowl does cool your bowl chocolate down and thicken it, as you're adding more beta crystals back into the bowl. So after each mold, you might need to just wave the heat gun over the bowl for a few seconds, whilst stirring. If you don't want to scrape back into your working chocolate, scrape into a second bowl, or even on the side of the bench, if it's clean ;)
Sometimes the darned things just stick. You have a whole mold except two come out easily. Sounds like you're on top of this, but just to say it for the sake of saying it - make sure chocolate is in temper :) If the molds are quite cool before you add the chocolate - warm them up with the heat gun, not so they're hot, just so they're not cold. Otherwise the chocolate that hits the mold first will likely stick to it and you'll have a hard time getting them out, even if the chocolate was in temper!
I'll just add - it's *really* hard to do things without the right equipment - I spent 5 months after my first class without a melt tank, just doing it all on the bench and with the microwave, and keeping chocolate in temper without something to hold it at the working temperature is practically impossible. So if you don't have a melt tank (if you're starting out, I can understand why you wouldn't as they are damned expensive, here in Australia at least), don't get discouraged, you just have to work fast and in small batches! I literally would only get 2 or 3 molds done before the chocolate had cooled too far for even the hair drier to help!