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Step 13Final boiling - when to stop
When your solution has been reduced by a little less than half (less than that if you're not sure), we'll begin removing very small samples to see if they crystallize.
Place several ice cubes or a quarter cup or so of crushed ice in a small bowl.
Using a clean cooking spoon (or small ladle), transfer a very small amount of solution (one to two teaspoons) into a clean custard dish or other small bowl; to watch for crystal formation, it's best to use a dark bowl.
Cool the custard dish containing the sample by setting it on (or holding it on) the ice (first picture). After a minute or so of cooling, blow gently on the solution to see if you can trigger crystallization. If nothing happens, you can either discard the solution or return it to the boiling solution. If you're not absolutely certain it hasn't been contaminated with dust or anything else, it's better to discard it.
Rinse the custard dish, shake excess water off (don't dry it with a towel or cloth), and take another sample after 5-10 minutes.
Eventually, you should be rewarded by seeing long, thin crystals bloom across your sample as shown in pictures 2 and 3, below (taken about 2 seconds apart).
As soon as you see this happen, remove the solution from heat and put a lid on it!
Set the crystallized sample aside and cover it with another bowl or with plastic wrap for the moment - you'll want to save these crystals to use them as "seed" crystals later, to trigger crystallization in the cool solution when you're done.
Place several ice cubes or a quarter cup or so of crushed ice in a small bowl.
Using a clean cooking spoon (or small ladle), transfer a very small amount of solution (one to two teaspoons) into a clean custard dish or other small bowl; to watch for crystal formation, it's best to use a dark bowl.
Cool the custard dish containing the sample by setting it on (or holding it on) the ice (first picture). After a minute or so of cooling, blow gently on the solution to see if you can trigger crystallization. If nothing happens, you can either discard the solution or return it to the boiling solution. If you're not absolutely certain it hasn't been contaminated with dust or anything else, it's better to discard it.
Rinse the custard dish, shake excess water off (don't dry it with a towel or cloth), and take another sample after 5-10 minutes.
Eventually, you should be rewarded by seeing long, thin crystals bloom across your sample as shown in pictures 2 and 3, below (taken about 2 seconds apart).
As soon as you see this happen, remove the solution from heat and put a lid on it!
Set the crystallized sample aside and cover it with another bowl or with plastic wrap for the moment - you'll want to save these crystals to use them as "seed" crystals later, to trigger crystallization in the cool solution when you're done.
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