Kryptonite Candy




About: Hi, my name is Britt Michelsen, I'm a Chemical Engineer especially interested in Computational Fluid Dynamics. To balance all the theoretical work I like to make stuff in my free time.

The only thing standing between you and your plan to rule the world is superman? Despair no more, just follow this Instructable in order to succeed. Because as you probably know Kryptonite is one of the few things known to hurt or kill superman.

OK, ok I'm exaggerating a bit... In this Instructable I'm going to show you, how to make candy that "glows" under UV light and looks like the fictional mineral from the superman myths.

For some time now, I've been playing around with Fluorescein, which is a dark red powder soluble in water and alcohol. It is commonly used as a fluorescent tracer. Though it is used e.g. in eye drops and biochemical research, it can cause adverse reactions (like nausea or vomiting). Because of this, even though only very small amount are needed I don't think it is safe enough for candy (and it is not easy to get).

Sadly most phosphorescent substances aren't classified as "food grade" (even though they are not toxic). In most "glow under a black light" food Quinine is being used, which is in Tonic Water (in very small quantities). In my opinion for candy it is not suitable thought, because of two major reasons: 1. the bitter taste and more importantly 2. it's melting point is very close to the temperature you will need to make the candy.

So I had to find an other easy to get food grade chemical with a high melting point. My solution: Riboflavin, better known as vitamin B2 or additive E101. It can be found in most vitamin pills, is not toxic and fluorescents yellow under UV light (and even under direct light). The only set back is, that it is destroyed by exposure to light, but in our case it should matter because the process is pretty slow. Btw. that is the reason why you should buy your milk rather in opaque containers and not in glass bottles.

OK enough with the boring science stuff, lets go kill superman ;-)

Becky Stern from MAKE Magazine made an amazing video, on how to make the candy:

Step 1: What You Need

what you need
  • 250 g sugar
  • A vitamin B2 pill (just ask in your apothecary, or on (half a pill is enough)) (the one I used had 15mg per capsule and I used three capsules, don't use more than that, it will not enhance the effect)
  • green food colouring
  • mint oil (or any other type of oil to give your candy a nice taste)
  • aluminium foil and/ or powdered sugar and e.g. quartz crystals (to make the forms)
  • UV light
  • a small pot
  • candy thermometer

Step 2: Make the Moulds

We will start by making the mould, you can use either of these two or both methods:

1. Making a mould with powdered sugar: pour the powdered sugar (or corn starch) into a casserole dish and carefully flatten it with a spoon. I've used quartz crystals to make the mold, by pressing them into the powdered sugar.

2. Making the mould with aluminium foil: Simply fold the aluminium foil to a form, as shown in the third picture.

In my opinion, the ones made with the aluminium foil turned out better...

Step 3: Cook the Sugar

I know that having to stand in the kitchen doesn't quite fit a future evil world leader, but I'm sorry you will have to endure this. It's better to cook with little light as possible in order for your plan not to get discovered

Start by mixing the vitamin B2 pill and 150 ml of water. Then you will have to add the sugar and slowly heat the the mixture, while stirring until it's boiling. Let it cook until it has about 300°F, add the mint oil and the food colouring and immediately pour it into the forms.
If you don't have a candy thermometer don't worry, you can find out whether you mixture is ready, by taking a spoon and letting a huge drop of it fall into cold water, if it immediately hardens and you can break it like glass, it's ready.

Making the candy with sugar is perfect, because to be classified as a true mineral, a substance must be a solid and have a crystalline structure. It's better to cook with little light possible, because light destroys Riboflavin, but considering the amount we are working with it doesn't really matter. As you can see it has a nice yellow colour, thats why it's commonly used as a food colouring.

Hints on cooking sugar:
If you are having problems with your sugar crystallizing, instead of having a nice clear result, try using a brush with a little bit of water and wipe the inside of your cooking pot with it until there is no more sugar that has crystallized. Best is, if you do this, after the sugar has stopped boiling at about 210°F.
Another thing you can try is to dip the pot into room temperature water, to immediately stop the cooking process, after the sugar has reached 300°F.

Step 4: Finishing Touches

Pour the sugar into the mould and let it harden. Make sure it has no sharp corners, before you serve it. I cut myself pretty severely into the thumb with it. Please, tell me if your evil plan was successful!

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    80 Discussions


    5 years ago

    ya. thanks for english version. I greatly appreciate it. once again still a great instructable.


    6 years ago on Step 4

    Hey! Did you make that uv led kryptonite or bought it?


    Reply 6 years ago on Step 3

    Just a few drops (about 3-5), the amount I used varied, because everything is going so fast.


    Yes, truffleshuffleboi suggested this, too. But adding it might be a bit tricky, because it is not a fluid. If you add it after the cooking process is done, I'm pretty sure it will result in crystallizing the sugar. It could be possible though to solve it in water and cook it with the sugar, but the melting point of citric acid is very close the boiling point of the sugar.


    Reply 7 years ago on Introduction

    I'm afraid you will have to experiment a bit. I don't think that substituting the water with lemon juice will work, because it will probably result in crystallizing the sugar. Maybe you can find an oil with a sour taste.

    use your fave OIL based flavor (dont use a water based one or the candy will seize up) you want sour (apple. watermelon. lemon. lime)

    then add any of the following
    *malic acid
    *tartaric acid
    *citric acid (easiest to fins at health food/candy/baking stores)

    use a 1/4 teaspoonof citric acid and put in during the flavoring stage and mix well.

    SOmehow I imagine Kryptonite should be toxicly sour and not toxicly offense BrittLiv.

    I'm definitely gonna make these and I'm gonna make them toxicly sour. thanks for the reipe!

    Also found outabout ascorbic acid...look up the intructable on sour gummy candies by sfhandyman....its just vitamin c and trader joe's sells a straight vitamin c powder u could try for the outside combined with a lil sugar to balance the tartness


    7 years ago on Step 4

    This is just awesome - My nephews will love this! Thanks for sharing!


    7 years ago on Introduction

    I have a friend that is really big into superman, nearing on obsessive. I am So gonna make these for him :p.

    You said you can use any type flavoring, correct?

    1 reply

    Reply 7 years ago on Introduction

    Correct. What are you planning to use? I would love to see some pictures, if you are making it