Vermiculite with slow cooker?

[Redhotsal]

I fourth the flame annealling approach too. Not sure that a slow cooker actually helps that much for the vermiculite but also can't do any harm. Be careful though - the vermiculite can get very dusty when it's hot  so dont' stir it all around very much. Make sure you have enough vermiculite around each bead - you'll need about 2inches all round to provide enough insulation to allow the bead to cool.

I too always had trouble with lentils when batch annealling. There are two things going on here:

Firstly - you've used a press to shape the bead and a press will always super-chill the outside of a bead which will really stress things up. You should bathe the bead in heat for quite a while after shaping to try and get the outside up to the temperature of the inside of the bead. This means you need to place the bead high up in the flame because you don't want to lose the shape you've just laboured hard to achieve by heating the bead too much.

That lentil shape makes for quite a flat middle of the bead so it will lose heat from the centre much quicker than a round bead will - this will also lead to a higher stress scenario.

Flame annealing aims to reduce the stress in a bead to a tolerable point before plunging it into the vermiculite. Although it's not a substitute for kiln annealing it will help to make your beads less stressy in the run up to your batch annealling. Here's how it works....

If you're on a dual gas torch, turn off the oxygen until you have a billowly yellow flame. If you're on a hothead take the bead up to the top of the flame and you can even cover up the air holes.

You are trying to bathe the bead in a soft flame which is around 500 deg c. Propane alone will provide this temperature. The idea is that you hold the bead in this flame for as long as possible so that the outside and the inside of the bead even out at around 500 deg (ish....). This is around the correct annealing temp for Effetre. You ideally want to hold the bead here for about an hour, but that's not a practical option so try to go for aound 1-2 mins in this yellow flame. In this time your bead will get coated in black soot, which will act like a little insulating jacket when you plunge into the vermiculite, so the soot is a good thing. You can just wipe it off so don't be concerned about it. After you have flame annealed for as long as reasonably possible IMMEDIATELY plunge your bead into the vermiculite. This SHOULD minimise the crackage of the lentils, unless of course they were cracked before they went into the Vermic. The flame annealing is good though as it gets the bead down to a reasonable temp (i.e. one where you won't get bits of vermic sticking to the bead) so you don't have to waver around in mid air wondering whether you are hot enough to prevent cracking but cool enough to prevent vermic bits sticking to the bead.

Hopefully this should minimise your lentil cracking.

[Les]

Great advice Sal

I also have a piece of fiber blanket that sits on top of my pot of vermiculite. It helps to keep the vermic. that little bit warmer too