Instructables

How to make rocket candy

Step 4: Cooking Process

Picture of Cooking Process
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Put the pot onto a stove and set it to about 150 Celsius while stirring constantly to dissolve the KNO3 and Sugar.
Before the "Crystal Mush" stage Do not use gloves! It may soak up and Ignite, case in point fusepaper...
Once all the solids have dissolved you can turn the heat up a bit.

Tip: if the solution starts bubbling up a lot simply turn down the heat and be patient.

Eventually there will be a red slop and once it starts having the texture more viscous than water this as James Yawn says the "Crystal Mush" stage now turn down the heat to 125 Celsius and put Gloves on.
Once you have passed this stage make sure you mix and stir the propellant a lot because it reduces bubbles of air making it more durable once done.
When it starts looking a bit like putty turn the heat down to 107 Celsius and continue to cook, if you still hear sizzling then there is still water in it.
Once the sizzling has stopped you can take out a small piece the size of a pea and roll it with your fingers.

Tip: Make sure that the Rcandy is covered by something while you are off doing other things so that if it does ignite there will be less damage.

If it feels sticky that's the moisture in it so continue cooking, if its easily roll-able and not sticky mash it flat and let it cool. Once cool bend it and see if it snaps if it bends then keep cooking the rest of it and do another test in a few minutes if it snaps and is brittle then it is ready for moulding and the Rcandy has finished cooking.
-Remember that the propellant is very Hygroscopic so it likes to suck up water from the air, I did a rocket that was supposed to have a burn time of 0.2 seconds and it went for 15 so keep it dry.
 
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You can also flick a tadbit of water onto the mixture to see if there is any water left. If it immediatley turns to steam, you know that the mixture is above boiling point, and it is not bubbling, therefore there is no water.
Tombini (author)  I_am_Canadian5 years ago
That would seem logical
I have done it, seems to work.