Introduction: Turn Romanesco Broccoli Into a Candle

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I'm a little bit obsessed with Romanesco broccoli. I don't particularly like to eat it, I just like to look at it. It's so beautiful and unique and looks more like a coral or a crystal cluster than a vegetable. 

I have wanted to make this candle mold for nearly a year now and finally I got lucky and found it in my local supermarket.


This Instructable shows you how to cast silicone molds of organic objects. It's a bit of a complicated process because working with vegetables, in the summer especially, will be challenging since vegetables ensconced in silicone rot quickly, and produce the worst, eye-watering smell. 

For that reason, the first part of the project has to be completed within 24hours, so before you start, make sure you have all the necessary supplies on hand.

Supplies

Part one of the project:

  1. Romanesco broccoli---------------
  2. Fast setting silicone rubber (condensation cure preferably because it's cheaper and takes shorter to set)
  3. Sulphur free spray paint (preferably acrylic like Krylon)
  4. Sulphur free clay (DAS is sulphur free) and alternatively, you can use Blu Tack (also sulphur free)
  5. Glue gun (optional)
  6. Spray on oil (cooking oil, WD40 or mold release)
  7. Plaster of Paris (500g minimum)
  8. Clear acrylic varnish 
  9. Melamine or plastic coated board 


Additionally, for part two of the project (the actual candle mold):

  1. Flexible silicone rubber (platinum cure, thin and self levelling would be best)
  2. More plaster of Paris and aluminium foil (optional)
  3. Candle wax, wax dyes, wicks
  4. Plastic pipettes, small disposable cups 

Step 1: A Few Words About Silicone

There are two types of silicone rubber:

Platinum cure silicone comes in two, same size bottles and you mix it 1:1, It's great if you don't have a degassing chamber and you need to create a highly detailed mold. It's very thin in consistency, so your mold won't end up with a lot of bubbles, it's also easier to find very flexible rubber (shore hardness 5A-15A).

Downside is the fact that it cures slower, is more expensive and very sensitive to sulphur. So you have to make sure there are no sulphur residues anywhere the silicone will come in touch with. Everything has to be sulphur free - clay, varnish, spray paint. 


Condensation cure silicone comes in one large pot and has a tiny bottle of catalyst with it. It cures fast and if you add more catalyst to the mix it will cure even faster. It's also cheaper. Downside is the fact that it's not so easy to find very flexible rubber, it's usually around 20-28A shore hardness, so not very flexible. Still manageable, but you might end up having to cut through the mold to release your candle.  


I ended up using both types of silicone.

For the first part of this project speed was essential since broccoli starts to rot quickly and the smell was overwhelming, so I used condensation silicone to make a mold of the raw broccoli.

I then made a plaster cast of the broccoli and threw away that silicone mold (the mold itself smells awful the minute you de-mold the raw broccoli and within hours the smell gets even worse and no amount of washing will help). 

For the second part of the project I used platinum silicone to create a candle mold. It's thin and flexible enough to just peel the walls down without risking any injury to the candle. 

Step 2: Prep the Vegetable

Start by trimming the leaves off the bottom. Use a small sharp knife and be careful not to slice through the florets. Trim the stalk to make the bottom part as flat and even as possible.

You can either spray paint (coloured or clear spray) the head or brush it across the entire surface with PVA glue diluted with water. Either methods serves two purposes: to seal the small gaps between florets to prevent the silicone from seeping inside, as well as priming the surface of the vegetable to allow the air dry clay to adhere to it.

Step 3: Fill the Gaps

There are large gaps at the bottom between the florets and they have to be filled with clay (or blu tack). Any larger and deeper gaps around the head of the cauliflower have to be filled with small amounts of clay as well.


You don't have to wait for the clay to dry, in fact, once all the gaps are filled, you should go ahead and pour silicone straight away. That way the clay won't dry out and wet clay will be easier to remove from the mold.

Step 4: First Silicone Mold

Prepare a round-ish tube-like container. You want the container to be big enough to hold the Romanesco, but small enough to keep the walls thin. Remember that this silicone mold will be used a few times only and then we will have to throw it out, so keep the mold small and the costs low.

Glue the tube to the board with hot glue. Hot glue will act as a seal and prevent the silicone from escaping. You can glue it with regular glue and seal the bottom part of the mold with clay if you don't have a hot glue gun.

Silicone pour:

Before you glue the container to the board, you have to spray the cauliflower with something oily. I used oil spray from a DIY store, you can use any oil you have on hand, even PAM spray will work. Spray it liberally.

Measure and mix the silicone following the manufacturer's directions and pour it in a slow stream into the mold. Leave it in a room temperature place to set for the required amount of time.

Step 5: Silicone Saving Recycling Method

If you look at the cross-section of the mold, you will see that it's inconsistent- thin at the bottom and thick at the top. When you make a 1-part mold out of this kind of shape (wide base, slim top) you can utilise a silicone saving method by recycling old silicone molds.

Essentially, what you do is this:

Grab any old or destroyed rubber molds (they have to be the same silicone type for this to work) and cut them into smaller pieces.

Then, you want to mix a small batch of silicone and pour it inside until it covers the bottom half of the cauliflower.

Let that silicone cure for a few hours and then go back to finish the mold.

This time, mix a batch of silicone rubber and only pour a small amount of it into the mold, then, carefully fill the outer side of the mold with pre-cut old silicone rubber. Use a spatula to push those rubber bits into the liquid silicone and cover the entire thing with another layer of silicone (there is no need to wait for it to cure this time). Add old rubber pieces to this layer of silicone as well and repeat this until you reach the top of the mold.


In the first picture you can see how I utilised this method, my old mold was pink in colour so all those small rubber pieces are clearly visible.

When you are done with this part of the project and time comes to throw this first silicone mold away, you might want to grab a knife and cut away as much of the outside rubber as possible and keep it for any future projects.

Step 6: Demolding

The silicone wasn't very flexible, so I had to cut two slits down the sides in a zig-zag pattern and pried the sides apart to get the broccoli out. Air dry clay was still wet enough to just scoop it out.

I then had to pick up any small bits of the Romanesco stuck to the inside of the mold and wash the inside with soap and water, then dry it out completely with paper towels.

I secured thick rubber bands around the mold to keep the cut sides from distorting the shape.

Step 7: Plaster Casts

Plaster of Paris cast:

You need to make at least two hollow casts of the broccoli, which, once set, will be going straight to the bin. The reason for this first and second cast is so the plaster can bond to any stray bits of broccoli left in the crevices, as well as any transferred spray paint leftover on the silicon. And even if your cast comes out perfect and with no stray bits of vegetables, you will still end up having to throw it out, because it absolutely STINKS of rotten broccoli.

The third cast, which is the one you will end up using, is filled to the brim with plaster and left to set for 2-3 hours. You should make a few additional full casts just in case you want to use them in the future.


How to make a hollow cast:

Mix a small batch of plaster of Paris using warm water (to speed the setting time) and fill the mold 1/3 of the way. Then spend 5 minutes rotating the mold in your hands to make sure plaster leaks into all crevices. It will pretty much thicken after 3 minutes and once it's thickened and spread around the entire interior, you can put it aside for 1 hour to set before you can demold it and start on another cast.


You can see the first plaster cast picked up a lot of spray paint deposit (it's speckled in red).

Step 8: Fill the Gaps and Varnish

There are several bigger and smaller crevices and undercuts in the plaster cast and they have to be filled. This step is necessary if you want to end up with smooth, unbroken candles, otherwise wax will get stuck in those spaces and break off while demolding.

I used air dry clay to fill in the larger gaps and sculpted it roughly with some small, blunt tools I had on hand. Smaller crevices were filled with E6000 glue (tinted blue for better visibility).

Final step is to apply a thin layer of liquid or spray varnish. Varnish is necessary to make the surface of the Romanesco uniform and smooth and it will make it easier to de-mold once the second silicone mold is done.

Step 9: Second Silicone Mold

Once your plaster broccoli is prepped, you can make a second silicone mold, this one for the keeps. Because of the shape of the Romanesco, there are a few ways you can make it. The easiest one would be to just cast it as a 1-part mold, just as we did in Step 3.

You could also make a glove mold, but this method requires more specialised products such as thixotropic additive, accelerator additive, resin, fiberglass matt and more.

I opted for a hybrid method of combining a glove method and a 1-part mold method which is both easy and cheap. It creates a thin silicone glove mold with a thick, sturdy, removable and level plaster base.

It's not the most elegant or the fastest method, but I chose it to show you that you don't need a bunch of specialised equipment or supplies to make your own molds, with this method you will only need regular, easy to find crafting products.

Step 10: Faux Glove Mold Method

First off, start by gluing the broccoli to the board. Regular glue won't work, but you can use a small amount of clay to fix it to the bottom. Grab a pencil and trace the outline of the broccoli onto the board.

Wrap the plaster cast in several layers of aluminium foil (4-8 sheets should do), you want to make a smooth, dome-like sculpture with no overhangs. 

Scrunch a long piece of foil into a snake and attach it to the base of the sculpture (you can use masking tape to help you secure it), it will act as a flange.

At the very top of the sculpture press a small tube shape like a milk bottle cap. You want it to protrude slightly from the sculpture. This will create an opening for pouring the silicone. Secure it with a masking tape.

Step 11: Plaster Mold

Create a round border around the aluminium sculpture and secure to the board with hot glue. Spray the sculpture with oil.

Mix and pour plaster of Paris into the mold. Leave the top part of the cap uncovered. You want there to be an opening in the cast. 

Let it set for several hours. 

Step 12: Mold Assembly

  • Carefully remove the plastic border from around the plaster mold, try not to disrupt it and use a pencil to outline the shape of the plaster mold.
  • It's very important to have both those shapes outlined on the board, so you will know how to arrange the broccoli and the plaster mold for when you are ready to pour silicone.
  • Now, lift up the whole thing, turn upside down and remove the broccoli from the mold and get rid of the foil.


  • Oil the inside of the plaster mold.
  • Arrange the broccoli and the plaster mold in a correct way on the board.
  • Oil the plaster broccoli.
  • Add a thick layer of hot glue or air dry clay around the edges of the plaster mold to prevent any silicone leaks. 


Step 13: Platinum Silicone Pour

Mix and slowly pour the silicone through the opening at the top. If it's self-levelling and self -degassing silicone, you will see a lot of bubbles rising to the surface and popping for a while after pouring, It's normal, don't do anything to the mold, just leave it be.

Leave it to set.  

De-mold, clean up the mold and wash silicone and plaster with water and soap.

Step 14: Candle Assembly

Before you assemble your mold, you want to take a thick needle and poke a hole at the top of the mold to make way for the wick. Then, you want to push a wick through the hole and leave a few cm hanging outside.

Step 15: Paint Splattered Candles

To create paint splattered candles or an ombre effect you need to dissolve small quantities of wax and dye in small containers (I microwave mine) and use pipettes to add colour splashes inside the mold. You have to work fast while the coloured wax is still hot and liquid enough to get into all the small spaces of the mold.

Once the outer layer of the candle is covered in coloured wax pour your large quantity of regular wax (white or dyed) mixed with essential oils and let it set for 12-24 hours before de-molding

Step 16: Finished

Step 17: Enjoy ;)