How to separate the melted rock candies

Have you tried using a marshmallow recipe that is only made from gelatin and cooked sugar syrup (sugar, water, and light corn syrup to soft ball stage, 240 degrees F)?

I have made various piped marshmallows that will hold swirly shapes using this type of marshmallow recipe. It is a bit more stable than the egg based recipes. The most important thing is to make sure that the marshmallow mixture is whipped to a nice fluffy, shiny, smooth stage (about 7-10 minutes on high speed) and piped very quickly into whatever form you want before it sets up using a large round tip. Timing is of utmost importance here and you may lose some marshmallow during this process at home.

I would also recommend piping onto a silpat (silicone) lined sheet tray or a piece of wax paper that has been lightly dusted with a mixture of cornstarch and confectioner's sugar.

As you mentioned it is all about how the crystals form.

Some of the factors off the top of my head:

• How saturated is the solution - The more sugar packed into the syrup the more easily it will crystallize.
• How quickly it cools - The slower the bigger the crystals
• Interference - Do you have a starch or other sugar molecules gumming up the works?

Obviously you already knew this from your question.

Not using other sugars will help. You might also try adding more sugar to the recipe at the beginning to fully saturate your solution. The fact that you add sugar at the end and it still dissolves in makes me think your solution could take a bit more. Letting the solution cool slowly with your seed sugar at the end should help.

You would think it would be easier to get it wrong. Perhaps you simply have too much experience doing it right.

Ask an amateur to try out your recipe and see if they fail properly.