Introduction: Exploding Death Star Bath Bomb

About: My name is Britt Michelsen. I am a chemical engineer from Germany especially interested in computational fluid dynamics. To balance all the theoretical work, I like to make stuff in my free time

In this instructable I am going to show you how to make a bath bomb that looks like the Death Star from Star Wars. Once placed in bathing water it will start to glow and make your bath a unique and fun experience.

I have always loved playing around with glow in the dark and UV light activated pigments and wanted to try this idea for quite some time. Since it will be Christmas soon and I figured that they would make a great gift I finally decided to give it a shot, not knowing how good they would turn out.

After a few iterations and a bit of experimenting I am finally happy with the result and ready to share it with you.You can of course make yours all black without the glowing effect, should you not want to modify a LED cube.

Step 1: Ingredients

For the bath bombs

  • 200 g baking soda
  • 100 g citric acid
  • 40 g corn starch
  • 45 g shea butter (*)
  • 7 drops of an essential oil
  • Star Wars Death Star Silicone Ice Molds (e.g. here)

For the lightning effect:

  • Neon Body Paint (e.g. here)(**)
  • Activated Charcoal (the cheapest I found was teeth whitening powder, e.g. here)(***)
  • LED Ice Cube (e.g. these); I couldn't find any with UV LEDs, if you do, please tell me where to get them.
  • Straw head UV LED


  • Thin saw
  • Soldering iron
  • Glue

(*) I picked shea butter due to its moisturizing and skin smoothing properties, but you can pick another type of fat.

(**)You can also use glow in the dark powder, but UV black light products are generally cheaper to purchase. Since we are using an UV LED cube, there is no need to get the more expensive powder.

(***) The activated charcoal is not just used for the colour, but also for its health benefits. It draws bacteria, poisons, chemicals, dirt and other micro-particles to the surface of skin, helping you to achieve a flawless complexion and fight acne [1].

You don't have to use the modified led cube, but the effect will be a lot less spectacular, since there is no way for the glow in the dark particles inside the bath bomb to get charged, so when you turn the light of before taking a bath the effect would be rather underwhelming. If you are further interested in learning more about glow in dark vs. UV light activated pigments, please check out this article.

Step 2: Preparing the LED Cube

Start by carefully cutting one of the LED cubes open, as shown in the pictures. Once you have cut along all four sites you should be able to take it apart. I decided to go with a cube that doesn't blink.

Unsolder the original LED and replace it with a UV LED. Make sure that the legs of your LED have about the same length as the original one and that you get the polarity right.

Once you are done, glue the LED cube back together and make sure it is properly sealed.

Step 3: Making the Bath Bombs

The recipe should be enough for about two and half bath bombs. I decided to make a bit extra to be sure that it is definitely enough for two.

Mix the baking powder, citric acid and corn starch. If your powders are rather coarse it is a good idea to use a strainer.

Afterwards melt 40 g of the shea butter, add it to the mixture, as well as a few drop of essential oil and knead everything. Separate it into two bowls, one containing 1/3 of the mixture and the other one the rest. Add about 10 ml of the neon body paint to the smaller amount and mix thoroughly.

Add about 4 g (or more depending on how dark you want your bath bomb to be) of the activated charcoal. Since my mixture was a bit dry I decided to meltand add 5 more grams of shea butter.

Step 4: Fill the Silicone Mould

As you can see in the pictures I used the black mixture on the outside, placed the UV LED cube inside of it and filled it up with the neon coloured mixture. Afterwards I filled the other half with more of the black mixture and pressed the two halves together.

I used the hole on the top to add even more of the black mixture to make sure that it was packed properly.

Since the mould started to open up I decided to use some tape to hold it together.

Let the bath bombs set in the fridge for about an hour or at room temperature for about 24 hours.

Congratulations you are done!

Step 5: Bonus Step: Failures

Like I said in the beginning, I experimented a bit. In this step I would like to show you what didn't work:

  1. Mixing the activated charcoal and the neon colouring in one go: Even though the appearance of the bath bomb wasn't altered that much the glowing effect after placing it in water was much less effective.
  2. 3D printing the mould: I originally wanted to make the bath bomb a bit bigger, so I decided to 3D print a mould. Sadly the bath bomb mixture stuck really well to it and I couldn't get it out.
  3. Wrong mixture: As you can see in the third picture, getting the mixture right is important. I didn't mix that batch thoroughly and it was too dry. So the Death Star fell apart when I tried to get it out of the mould. Don't worry the mixture I am showing here worked really well.
  4. Trying to film the bath bomb with a GoPro: As you can see in the gif underneath, the charcoal particles and shea butter fogged up the lens. So the effect of the bath bomb can't really be seen (the gif is sped up):

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Baking Soda Challenge 2017

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