TUTORIAL: Making Moulds and Casts

cardyfreak

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Here are my tutorials on casting. Ill update this as I add more. At the moment I have an introduction, how to make an open faced mould tutorial, and how to make a two part mould. I've got PDF versions also, but I can't attach them from my phone. Ill sort it out when I get on my proper computer. Either that PM me and ill email what ive got to you. Ive done it all on my phone so the formatting isnt great but hey, we cant have it all. Enjoy!

Many of the techniques I've used are gleaned from many sites on teh intrenets. rubbishinrubbishout on YouTube has some excellent video tutorials on this subject; it is basically where I learned how to do this. Also check out the hirstarts site for some great tips about all things casting. This article is really just to pull everything I've learned into one place for convenience.

Please bear in mind that many of the principles of two part moulds are the same as open faced moulds. I recommend familiarising yourself with the principles of moulding by doing a few open faced moulds before progressing onto two part moulds. The open faced mould tutorial has all the photos you need to guide you, and these also apply to two part moulds. I have left out quite a few photos of the steps of two part moulds so as not to incur any copyright enforcing wrath, so again, a good understanding of the principles of moulding is important.

There will be little tips after each guide from people asking questions, so I'd recommend reading those also. But if you have any questions at all, please ask. It'll save you a shit load of silicone if you are confident in your mind that you know what you're doing. Believe me, I've wasted a fair bit!

Some people have asked where I buy my silicone from; all of the materials I use in these tutorials are from DWR Plastics. I can thoroughly recommend him, he ships quickly and the very few issues I have had have been resolved extremely quickly and very satisfactorily. He also trades on eBay but it's cheaper buying direct from the site.

2 part tutorial starts at post #29
 
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cardyfreak

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Making Moulds- Introduction
by cardyfreak


Making moulds of objects and casting them might seem like a complicated process but it is a lot easier than you think. Sure, you need to take a bit of care to get the best results but that is true of most things.
Having the correct tools to hand is probably the most important piece of advice I can give. Particularly when casting, time is of the essence. You don't want to be rummaging around for things at the critical moment when pouring silicone or resin so always make sure you have everything you need laid out in front of you neatly. When your mould tips over and resin starts pouring out all over your table, you'll be glad you can lay your hands on some kitchen towel without having to go rummaging through the kitchen!

The basics

Here is a list of some common terms and their definitions as I understand them. They might be incorrect, but I'm pretty sure they're close to what's right.

RTV silicone- Room Temperature Vulcanising silicone. This is a type of rubber. Most master and production moulds are made out of organic rubber. These are very hard wearing and are used to make many casts of a shape using low melting temperature alloys, traditionally pewter or other lead alloys. This is a bit excessive for what we need, so The Lord giveth RTV.
Also know as 'condensate cure silicone', RTV uses the moisture in the air and/or an additive catalyst to cure (vulcanise) the silicone rubber into a solid shape. Places with high humidity cure faster than ones with low humidity, and the exposed surfaces will set first. However, some silicones with a catalyst will set at a uniform rate. If we pour silicone over an object we can make a mould.
Depending on how much catalyst we add we can vary the stiffness of the finished mould. Your RTV will generally come with mixing instructions for varying ratios of silicone to catalyst.
For reproducing figures and fine detail we should use the minimum amount of catalyst advised as this will make a softer mould that is better suited for capturing fine detail and easy release of the cast item. For larger moulds we should use more additive to make the silicone stiffer as it will maintain a uniform shape and reduce the chances of warpage across the mould. So for minis use a low mix ratio, for terrain pieces like bulkheads and larger use a higher ratio. If the ratios are incorrect the mould will fail. Too little catalyst and the mould won't take shape properly. To much and it will be brittle and difficult to de-mould without tearing.

Mould- This is what we use to capture a shape and subsequently reproduce.

Cast- The process of reproducing a shape using a mould and casting material, and the resulting product.

Casting Chamber- A box or other shape that is used to contain the silicone whilst it sets. Can be made from a variety of materials, including Lego, foamcore, plastic and cardboard.
Foamcore and card are fine for open faced moulds but I find them a little bit of a pain to use as two parter casting chambers as they can break apart when releasing the first stage of the mould, and recreating the exact shape of the mould can be difficult. Lego gives you a constant size and shape to work with, making your work neater and giving you more confidence with the materials at your disposal. Head to the local Lego shop and buy some bits. Get a base piece and a bunch of 4, 3 and 2 stud pieces, with a couple of ones for versatility. A small tub and base costs about £11. That's what I've got in the example below. I can make about four casting chambers from a small tub, to fit one mini each.

Resin- Polyurethane resin is a common casting material. It's more expensive than plaster but sets a lot quicker and harder. It's ideal for casting figures and capturing fine detail. Use gloves when handling this stuff cos it's a swine to get off your hands!
Resin generally comes in two parts, the resin and the hardener. These are combined (usually a 50:50 ratio) and a chemical reaction takes place causing the clear resin mixture to go hard and opaque. This is why the thicker parts harden first; the chemical reaction is stronger in these deep sections. You'll notice if you make bases that the centre will cloud over before the edges. This is the reaction at work. It is an exothermic reaction, meaning it gives off heat. You'll feel this through the mould when you cast.
Also, resin leeches the moisture from the mould and over time will perish it. We can counter this to some degree by using release agent and mould nourisher to protect the mould but eventually it will become unusable. You should generally leave a mould for about a week to finish setting up if you want to cast using resin.
Other resins include epoxy and acrylic.

Pot Life- This is the amount of time you have to mix and pour the silicon or resin after it has been combined with the catalyst/hardening agent. The more catalyst, the shorter the pot life.

De-mould Time- This is the amount of time you have to leave the casting material to set before taking the cast item out of the mould.

Release Agent- A silicone or wax based product we coat the mould in to protect it and ease the release of a cast. Also vital for making two-part moulds, as the only thing that will stick to silicone is silicone, so the release agent acts as a barrier between the two faces of the mould. This will be discussed later.

Plaster- Everyone knows plaster. Plaster of Paris will work perfectly well in moulds, but is very brittle and takes a while to set. Generally I would advise not to use Plaster of Paris as we need something more robust. Better still is Dental plaster. This is the stuff dentures are made out of. It sets rock hard and is really cheap- less than £20 for 25kg. A general rule is if has the word 'Stone' or 'Die' in it, it'll be rock solid when it sets. Notable British plasters are Diestone, Herculite and Crystacal.
This suits terrain casts more than miniatures, but some plasters can capture fine detail. They can be quite heavy compared to resin. Plasters will not damage the mould in any way, and can be used in a mould immediately as compared to resin, where the mould should be left for about a week.

Open Faced Mould- This is a one piece mould where the casting agent is poured into the top of the mould. Best suited for simple shapes like bases, barrels, barriers or single sided bulkheads. Care should be taken when selecting an object to open face mould to ensure the object doesn't have any significant overhangs. This would prevent the original object from being removed from the mould so you'd know if this happened.

Two Part Mould- This is a mould that has two pieces, or 'faces', typically capturing the details of the front and back of an object. This is better for moulding complex shapes. Most of your miniatures will have been cast like this. The telltale sign is the mould line running around the central axis of the mini. This is where the two faces of the mould meet. Care must still be taken when selecting candidates for this method of moulding. One piece mini's with no gaps through them are ideal; for the sake of example, Cawdor or Van Saar. But the newer range of necro minis with the optional weapons wouldn't be any use if the weapons were attached. The silicone would get between the mini and the weapon and would stop the mini from being released from the mould. The solution to that would be to not attach the weapon before making the mould. Gaps between the legs are fine, it is only gaps between parts of the mini which would make de-moulding impossible that we have to look out for.
 

cardyfreak

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Making an open faced mould
by cardyfreak


In this tutorial we will make an open faced mould of some generic barriers. Barrels are also good candidates for this method, as are bases. I would also advise making a few open faced moulds of scatter terrain and bases before moving onto two part moulds.
Not only are they easier to make, it will familiarise you with the process of mould making without wasting silicone on futile two parter moulds, and it's good practice to keep these handy when casting minis and what not because I always mix up too much resin and can pour the excess into these moulds to make more terrain. This way you'll waste nothing and end up with loads of scatter!
a8a2enup.jpg


Clockwise from the left-
Silicone spatulas & syringe
Measuring cups (my cup is marked in 50ml increments by pouring water in and marking the level)
Silicone and catalyst (the little bottle with blue stuff in it)
Release agent
Lego
Lego base
Card
Superglue
Disposable brushes
Paper towels for clean up

The syringe is used to measure the catalyst.

The superglue is used to secure the object to some card to prevent it floating in the silicone. It only takes a few dabs, you want to retrieve the object afterwards!

Use cheap brushes! This process destroys them
 
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cardyfreak

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Now that we have our tools out let's get cracking.
First, secure the object you wish to mould to a base of card with a few dabs of superglue. Don't use too much, it's purely to stop the object floating around in the silicone.
ga7aqebu.jpg
 
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When it's secure give the object a coating of release agent. If its a spray, give it a spray. Mine is brush on stuff so I just brush a coat on. Leave it to one side for about 10 minutes to let the liquid evaporate, leaving the release agent coating the object.
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Meanwhile build the Lego casting chamber around the object. Try to arrange the bricks so they always overlap, just like the bond of a brick wall. This will help prevent silicone seeping out. Build it high enough so there's two rows above the top of the object.
esadezeh.jpg
 
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cardyfreak

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Next, measure the internal dimensions of the chamber. This casting chamber measures roughly 60x70x30cm. Ive rounded all measurements down to compensate for the slight displacement the barriers will have. This means the chamber has a volume of 126cm3. To fill it we need 126ml of silicone because 1cm3=1ml. If we were doing this by weight, we would multiply the density of the silicone (1.08g/cm3) by the volume of the chamber (126cm3). 1.08x126= 138.8g, so round it down to a neat 138g. We would need 138g of silicone to fill the mould.
If we were casting a large object we would have to factor in its displacement. This is done simply by calculating the volume of the object and subtracting it from the volume of the casting chamber.
 
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Now pour out the required amount of silicone. From now on we are trying to eliminate as much aeration of the silicone as possible. This is very important, as air bubbles in the silicone can ruin the mould. The most important technique is the way you pour the silicone. Aim to have a long, thin stream. This will pop any large air bubbles that are in the silicone. Whenever you dispense silicone, always use this technique.
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Now add the catalyst. Seeing as this is terrain and its shape has no overhangs so it should be easy to de-mould, I'm going for a 100-4 mix ratio. This will give me a stiffer mould, but a much shorter pot time to work with. I use the syringe to add 5mls of catalyst to the silicone, giving me a pot life of 10mins.
uze7etaz.jpg
 
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From this point on, time is against us. The catalyst is now making the silicone react, so we must act swiftly, but we need to stir the two liquids together to mix them. But don't rush. It's not a mad panic or anything, and if you start stirring the silicone too hard you'll introduce loads of air into it. Stir the mixture so it becomes a uniform colour with no streaks and marbling in it. Don't worry about a few air bubbles, we'll get those when we pour. My catalyst has a blue tint but some catalysts are red, pink, green, all sorts of other colours. This is just a visual guide to help you mix the stuff correctly.
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Now that it's mixed, brush some silicone onto the object. This isn't strictly necessary but it's a good habit to get into, especially for when you start making complex moulds. This ensures you capture any detail.
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With that done we can pour the silicone into the casting chamber. Start in a corner and pour in a long, thin stream. Don't pour directly onto the object, you're likely to get air pockets. Rather, let the silicone flow up and around the chamber. This will push the air out naturally, leaving no air pockets. As the silicone flows you can follow it about with the stream of silicone, but try not to let it pour directly onto the object.
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And that's it! Leave it overnight to set, don't be tempted to poke and prod it or you'll ruin the mould by distorting it. LEAVE IT ALONE! If you see bubbles on the surface, a short, sharp blow of air will pop it.
As you can see, we have no excess silicone in the cup. When it sets it peels off the cup and silicone stirrer with ease. The brush with the silicone on it is useless now. The one with the release agent on is fine. I'd recommend giving it 12 hours at least before de-moulding.
yjy7e8e4.jpg
 
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I've left the mould for 12 hours so now it's time to see what we've got. Remove the casting chamber. You might see that the silicone has seeped underneath the card, don't worry this just trims off.
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cardyfreak

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Now peel away the card or whatever you glued the object onto. If the objects don't come out with this, just flex the mould a bit to get them out. If any silicone has seeped between the card and object, trim if away carefully with a hobby knife. This stuff is very easy to slice through so take a bit of care.
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Et voilà! You have a mould! I like to trim away all the loose stuff and cut a slight bevel along the sides with a pair of scissors to make it look neater. You can cast immediately with plaster, but you should wait a week to allow the mould to fully cure if casting with resin. Good work!
e4yruve4.jpg
 
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Fantastic guide. Thanks Cardy. Will begin looking into this next week I think for beginning to accrue some supplies for it.

The brush that you used for silicone, is it possible to wast this straight away or somthing to rescue it enough to use next time (similar to how you can with pva)? otherwise are you effectivly losing a brush each time you do it?
 

cardyfreak

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You'll need white spirit or a substitute to get the silicone off, the same goes for cleaning up silicone. Silicone repels water so it would just pour straight off. But I get like 20 brushes for £1 so I don't really care about going through them. They're no good for painting that's for sure!
I hope the tutorial is clear for everyone, I included the first introduction just to familiarise people with the concepts and process' a bit. I like to know the underlying mechanics of what I'm doing so I thought I'd add it in for anyone else. It saves googleing for hours if its in one place!
 

cardyfreak

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I get mine off eBay from DWR Plastics. Type seller:dwrplastics into eBay and his stuff will come up. He's sound, i asked for data sheets and he emailed them straight away. Everything in the tutorial is from him- silicone, resin and release agent. When you buy the normal resin you can buy additional colour pigments also. The red could be handy for certain robed fanatics :) You can get black resin too. You can also get fillite powder for bulking out the resin. I don't have any decent scales so I haven't really used my fillite much but it's not essential though.