Botanical Relief Casting in Plaster

As if I haven’t used botanicals enough in my art & design! How amazing it is that capturing nature’s form can be so beautiful! I am not going to tell you how… just kidding! Here we go; Botanical Relief Casting in plaster (and concrete as well)

Simple Supplies:

I was so happy to realize that I didn’t need anything that special for this. Doesn’t everyone have some plaster of Paris and plasticine at home? Simple children’s modelling clay works great for this project. This would also make a great project for summer camp as it will help create an awareness of nature and easy materials to use.


  • Modelling Clay (oil-base Plasticine)
  • Botanical Specimens
  • Rolling Pin
  • Wood Thickness spacers (not shown) opt
  • parchment paper
  • clay cutting tool (knife or similar)
  • Stiff board or tile
  • Frame shape (may use pre-made containers)
  • Plaster of Paris (or for harder casts Hydrocal)

The Pretty Plants:

I have a simple garden with a lot of variety but it’s by no means huge! This art form uses the form of the plants so it is better to choose ones that have some good texture or interest. There really are no rules! Once you start you will want to try them all! It is even interesting to show the roots or the bulbs! Try to have some type of design plan… Hint: if you can’t use the plants right away stash them in a container in the fridge.

The Frame Shape:

You can make any frame shape that you like… For simplicity I like to up-cycle some containers so that I have less ‘futzing’ with wood pieces. I also like them to be somewhat flexible to allow easy removal after casting.

These are a collection of my ‘frames’; store-bought cake container, storage containers cut, and even a chocolate box with middle cut out. I like that they are quite exact and can be cleaned. They are also transparent for some ease of use later…

Step #1 Make the base

Flatten an area of the clay with the rolling pin to a uniform smooth thickness on top of some paper or thin card board. This is important later so that you can lift the clay! The clay does not dry out and will be softer if it is warmer. You can use some heat like the sun to make it easier to flatten. If you like to use some strips to ensure consistent thickness at the edges that helps too! I plan to use some 1/2″ wood strips. Make sure the clay area is larger than the frame you want to use.

Step #2 Imprinting the design:

Arrange the botanicals as you like on your readied base of rolled modelling clay. You can place them all or work one by one. I like to arrange how they curve etc and hold in place before rolling over with the rolling pin. A sheet of parchment paper will help to make sure it does not stick. If the material is quite stiff and thick you may need a stiff board to push down the botanicals. I use a piece of clear plastic so I can see the design through.

Hint: the back sides of the leaves usually have more texture so face them down. If you want to make a change you can start over since it’s just reusable clay that does not dry, just flatten well again.

Once you rolled out the specimens they will be pushed into the clay. Flowers are nice but are be very very thin so the impression is very subtle. These bleeding hearts are quite dimensional! Be careful to keep the background as flat as possible for neatness.

Step #3 Pulling it out

I love the Bleeding hearts as they do have some interesting form in the flowers but there are many many more as well. Checkout all the kinds of weeds around… Spring & early summer usually has much budding going on.

Once you are happy with the design and have tested how it fills the frame carefully pull out the botanicals. They do come out quite easily since the clay is oil based and the plants are not. It is amazing how much texture appears! Use a low light source to see the details best. Use some tweezers or toothpicks if small parts get stuck.

Step #4 Shape of the frame

Whatever frame shape you decide can now be pushed into the clay. This will hold the plaster and create a mold so make sure it is well imbedded. If needed fill any of the openings like the stems that could leak with some clay bits from the outside.

Step #5 Pour your plaster

Mix up enough plaster to fill about 1/4 inch or more of the framed relief you have made. It is not vital to be a specific thickness. Some plaster is softer than others. Some also seems to have more bubbles…

Note: I have moved from using the cheap DAP plaster (as it was having many bubbles) to Hydrocal as it is much harder and less bubbles. You may practice with plaster to get the hang of it. Ultracal is even harder if you choose. I will also be casting in concrete… (soon)

Mix the plaster by first filling the water (flexible vessels like sour cream containers work well) and then keep adding the plaster until it sinks no more. Wait until it absorbs the water and then stir until smooth. Tap the container to rid of bubbles. Pour into the prepared frame.

It is also important to keep things level for uniform thickness. Lift the filled piece and tap it (lift entire stiff board) to make bubbles rise. The stems are quite thin voids so bubbles need to escape there. I have found that I prefer Hydrocal over plaster of paris since it is much harder.

Step #6 Pull from mold

I hope you remembered to put the clay on top of something flexible like paper. To lift the mold carefully pull the clay back from the plaster. You can slowly curve it away from the plaster form. Be ready to be amazed! ‘Or realize that you need to get all the bubbles out of the plaster. If you are careful when pulling the clay off the plaster you can usually cast another one from the same clay…

Since the plastic ring (from store-bought cake cover) is flexible and slightly tapered it come off easily. Any imperfections can be sanded with sand paper (do wear a dust mask for the plaster dust)

I never tire of how how much detail nature has! Now there is even much more reason to slow down and really look. So many plants have interesting shapes and textures not to mention when they have seed pods etc.

The Magic of Nature!

Flowers are very pretty but quite delicate. It may take a bit of extra pressure since the flower heads are thicker. Take a walk through the wild flowers and weeds; there is so much texture design that Mother Nature offers you.

This is my climbing hydrangea with spring buds. As with any art there is a million ways you can arrange and design the piece.

I am no stranger to using leaves but I had never realized the tactile amount of detail. I am now obsessed (no surprise) to make a huge variety and cast them in … CONCRETE! Yup, you guessed it! I am hoping to have some up for sale soon since I probably have too many!

‘And I haven’t even added colour yet! I do like the simplicity of colourless since then it’s about the relief textures. What do you like best? Colour or no colour? Plaster or concrete? Please add your comment below

Lots of effort and supplies go into making a process that works… I appreciate any sales of these through my shop

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  1. about to try making this. How long do you leave the plaster on the clay mold before lifting the clay away?

  2. I’m having a hard time with smaller flowers. Have you ever tried spraying the clay with oil so the delicate or smaller flowers do t stick?

    1. Oh, I had a few seeds get stuck and use small tools to pick them out. I have not tried any oil, I’m also thinking of a dusting of something, maybe like a talcum powder. It would be good to have a small piece of clay to test with some of the flowers. It might also be about the temperature of the clay since it gets softer when warm.

  3. Thank you for the instructions Barb! These are beautiful! I will be trying this soon and hope the ones I make turn out like yours.

  4. What an imaginative technique! I’m going to try it with acrylic paint skins instead of plaster so I can use it in collage.

  5. I’ve been trying to do this all summer & im at my wits end😢I’ve used regular clay & plasticine clay. I can’t get enough leaf print to show up for the plaster to catch if. The only thing that worked was chives & asparagus. Every leaf no matter what, looked beautiful in the clay but the plaster didn’t pick it up. It’s so much work to have if dud on me over & over. I pushed it down w rolling pin over a piece of plastic etc. The plasticine wouldn’t warm up & was awful to roll out.. bout killed me 😂. Maybe I’m just too old. I love how beautiful your pieces come out 😍

    1. I am so surprised! I know that the flat regular leaves don’t leave much impression. I would inspect every plant around my house to see how dimensional it is. I used hosta flowers, and other more defined plants. To warm the plasticine I also had it in the sun. Maybe a heating pad or hot water bottle under the board will warm it to be easier. Sometimes instead of trying to roll out a block I would cut slices and spread it by ’tiling’ those together, then rolling. Succulents were some of my favourite ones to use. Oh, BTW, I am old too… I hope you don’t give up.

    1. I tend to just ‘wing it’ but there are more calculated ways. Once I’d have a ballpark amount I’d mark my mixing vessel. Here is a tool to calculate. ‘Hope it helps!