How to make a Simple Single Part Mold

Hi Folks,

We’ve all been there, desperately rummaging through our bitz box to try and find the 3rd widget, only to despair at the inevitable conclusion that we’re going to have to resort to paying over the odds for the extra piece you need from one of those online bitz suppliers. You log on, bringing your credit card to bear, telling yourself that £3.50 for a Storm Shield isn’t too bad… then – Out of Stock… Every. Single. Time.

How familiar is that for you? Quite, I reckon. You my good friend, need to learn the mystical art of casting.

In this tutorial I’ll teach you how to make a simple single part mold without the expensive RTV silicone. There are limitations to this method, namely that you can only cast one side of something. So it typically works well for shields, icons, and bases etc. If you want to cast something with many sides, like a Boltgun for example, you’d need to use a two part mold. That’s slightly more advanced and I’ll cover that at a later date.

The very first thing you need to do is buy yourself some Oyumaru (bless you!), this goes by different trade names such as Blue Stuff or Instant Mold, but if you’re clever, you’ll find it in greater quantities, and cheaper under its proper name. (Try eBay!)



You also will need some two part epoxy resin like material. I tend to use Milliput Standard, because it’s easier to sand and shave when it’s cured. But you could use Green Stuff if you prefer.

Finally, this is easier if you have a small plastic lidless box that’s just larger than the piece you want to cast. This is not completely necessary, but it does get better results. I use Lego bricks to achieve this because I can rebuild them in different shapes as required!


I’ve covered this before in my How to Make Dungeon Tiles series, but it was a while ago, and my methodology has improved so I’m going to do it again!

Boil the kettle, pour some of that boiling water into a mug. Don’t burn yourself!

Dunk your Oyumaru into the boiling water, rest a fork on top of it to keep it weighted down. Leave it for about two minutes.

Fish your Oyumaru out using the fork. Give it a squidge. If it’s still solid in the middle, leave it back in the water for a minute or two. Don’t burn yourself!!!

When the Oyumaru is fully malleable, that means it’s ready. Take it out of the mug, and squidge it around to make it into a blob, then fit it into your lego box. Try to get the top as smooth and flat as possible. Time is of the essence here, the Oyumaru is setting as it cools!

Lego box

My Lego ‘box’

Take the piece you want to cast, then, detail side down, press it into the Oyumaru, applying firm and even pressure. Make sure that you push it down far enough to capture all the details, but not so far down that you get an overflow over the top. The purpose of the box is that it stops the Oyumaru from escaping sideways, giving a crisper mold around the piece you’re copying.

Cracked earth base

This is the piece I’m casting

Once your piece is set in the mold, take the whole thing over to the tap and run it under cold water for 30 seconds. This will set the Oyumaru and you can follow up by removing your piece leaving just the mold with the imprint. You should also remove the set Oyumaru from the Lego box at this point.

Oyumaru mold

The finished mold

Well done, you’ve made a mold!

Casting with it is simple, just take your prepared Milliput, judge the correct amount you need, and press it into your mold. Wet your finger then use it to smooth the surface of your putty, push away any excess and remove this waste as applicable.

Oyumaru Mold

Casting Milliput

Set the whole item down, away from things that can contaminate it such as cat fur, or children, or cat children… leave it 12 hours then gently flex the mold and push your casting out with your fingers.

Beware the Cat Children

Beware the Cat Children

If you’ve used Milliput, you can very easily use a hobby knife and files to clean up your cast , removing any flash etc that may have formed. Personally I think this stage is more difficult if you use Green Stuff, but your mileage may vary.

My new cracked earth biker base

Milliput Cast

Well done, you’ve cast a piece!

Oyumaru molds can be used many many times, and once you’re done with a mold you can simply reset it in boiling water and start the whole process again with a new bit to copy.

Be aware that because of this you shouldn’t store your favorite mold it anywhere where it will get hot, this could ruin your mold by turning it into an amorphous blob.

Right  then, I hope you’ve found this guide for making simple single part molds useful, let me know how you get on in the comments below!



If you like this guide, you might also want to check out my others for how to use Quickshade Dip, or how to use Hirts Arts Molds. Alternatively check out my reviews on this MDF Paint Rack, or Textured Rolling Pins.


When you cast copies of some company’s bits, you’re generally not allowed to sell them on. That’s a breach of copyright. Here in the UK, you can take casts of things as long as it’s for personal use only.

Check your local laws if you’re in any doubt, I’m washing my hands of any responsibility!!!

2 thoughts on “How to make a Simple Single Part Mold

  1. Pingback: How to Print and Apply Decals | Jimmi Waz 'Ere

  2. Pingback: How to make a Simple Two Part Mold | Jimmi Waz 'Ere

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