Notes on Epoxy Putty

On some forums I regularly see members who are curious about learning to sculpt and the materials needed, particularly epoxy putty. Having had some experience with different types of putty, I usually pipe up, and usually with the same long description; so I decided to post it all here
In this I’ll only deal with putties I have first-hand experience of, so this review is basically a compilation of rough notes for a more comprehensive guide. Also, there may someday be reviews on polymer clays and a proper sculpting tutorial, although there’s plenty of help available for the latter anyway. Please see the links at the end.
I’ve separated the different putties into two basic categories: elastic putties and epoxy clays. These are my own definitions, based on their cured and uncured states. Elastic putties have a texture that is something like chewed gum or sticky tack, and stretch to an extent when uncured. They cure to a slight flexible, rubber/plastic-like state. Epoxy clay is appropriate as the putties in this category act a lot like clay; more so than elastic putties, at least. They're water-soluble to some degree, and cure rock-hard. They're also usually cheaper by weight.
Lastly, before we start: if you’re a lucky git, like me, you shouldn’t have any problems handling putty (although I wash my hands well after using it). However, some people can have skin reactions after handling certain putties, making the use of gloves necessary while handling it or even preventing the use of said putty. Which type provokes a reaction in which person is largely pot luck; but those with a history of sensitive skin should be cautious.

ELASTIC PUTTY

Green stuff
The old workhorse. Probably the most used and familiar epoxy putty; so much so that original sculpted miniatures are commonly known as ‘greens’, despite the fact that other putties may have been used. This is officially called ‘Kneadatite Blue/Yellow’ by the manufacturer, Polymeric Systems, and in Europe is sometimes known by the repackaged name Duro.
Like the official and popular names suggest, this putty comes in two parts, blue and yellow, which magically mix together to make green. It’s packaged as a strip, with the two parts side-by-side, and in a tube, in which the two parts are separately wrapped bars. The two parts in the strip can cure where they touch and leave hard lumps in the freshly mixed putty, although this is usually solved by leaving a few millimetres in the middle of the strip, where the parts meet, when cutting off pieces to use. The tube, marketed to miniature sculptors and hobbyists, pretty much bypasses this problem.
The freshly mixed putty has a consistency a lot like chewed gum, except maybe a little stiffer. It’s quite sticky at the start, and it’s usually a good idea to leave it for a few minutes before working, or concentrate at sticking it on first. When sculpting, it has a slight elasticity, causing it to ‘spring back’: known as memory. This makes it more difficult to achieve sharp edges (more so than any other medium I've tried), although continual reshaping helps, and the property is useful for organic, rounded shapes. It has a working time of around 1-2 hours, depending on factors like temperature and mix ratio.
The cured putty is somewhat rubbery and flexible. It can be drilled or cut at this stage, but not cleanly, and it doesn’t take filing or sanding kindly.
Different ratios of each part create some differences. More yellow in the mix makes for a softer, sticker putty with a longer working time and more flexible cured state. More blue means the opposite: stiffer, shorter working time and a harder final state.
One small problem with green stuff is that it goes ‘stale’ after a few months. It becomes harder to mix, less responsive when sculpting, and may not cure quite right. There are a couple of ways around this: one is to store the unmixed green stuff in the freezer until needed. I’m not sure if other elastic putties have a longer shelf life, or if they go stale at all, but if they do I haven’t noticed it.
Freezing also delays freshly mixed green stuff and some other putties from curing, indefinitely.

Brown stuff
Also manufactured by Polymeric Systems, as Kneadatite Brown/Aluminium or Brown/Neutral. This is packaged as a short strip in a small plastic case, although the two parts don’t touch, and costs more per weight than green stuff. That’s okay. I feel its properties are suited towards detail rather than bulking and building up, anyway. To use an analogy, brown stuff is for the plasterwork of a house, not the foundation.
The freshly mixed putty is a little softer than freshly mixed green stuff, but the main difference is that brown stuff has virtually no memory; at least in comparison. Straight, sharp edges and details are very easy to achieve with a little work (I giggled like a maniac when I found how easy), and sculptors swear by it when making weapons, mechanical objects, small and intricate details, etc.
Cured brown stuff is harder and much less flexible than cured green stuff. I’d say it’s close to an epoxy clay, except that it does tend to bend and rip rather than snap sharply. Nevertheless, it is easy to dry sculpt. It’s easily filed, sanded, cut and shaved, which makes it even more useful for sharp and mechanical details.

ProCreate
A recent addition to the market, this is produced by Kraftmark, and packaged as two foil-wrapped bars - dark brown-grey and white – in a blister pack. It has a daft name, but you get used to it despite Kraftmark’s sense of humour (no-one seemed interested in nicknaming it ‘grey stuff’, anyway).
Unlike the previous two, this was originally formulated for miniature sculptors, with both beginners and professionals in mind. It claims to combine or reproduce the properties of green stuff and brown stuff, becoming more like either depending on the ratio in which you mix it. I.e. more hardener for organic shapes, more resin for sharp edges. I don't know so much about the different ratios, because it's a little different to either of those putties no matter how you mix it. I would guess it’s mostly due the stiffness of the hardener and softness of the resin
The freshly mixed putty is very sticky. In my opinion it’s even more important to wait a while with this, before trying to sculpt any shape or detail. Shape and detail are then easy to achieve. It does combine some of the properties of green stuff and brown stuff. It lacks memory, like brown stuff, which makes it useful for detail; but is also easily sculpted into curved shapes, thanks in part to a property that makes it surprisingly easy to smooth (I giggled like a maniac. Again.). Also, the light grey colour makes it easy to see any detail you’re sculpting, and the uncured putty is very slightly water-soluble, which aids smoothing, cleaning, etc. It has a long working time, about 2-3 hours. Again, this is dependent on temperature and mix ratio.
Cured, it's still quite rubbery in my experience, despite claims of properties like brown stuff. As much or more so than green stuff.
The uncured properties I described are the reason Kraftmark says it’s suitable for beginners. I can believe it. If you’re used to green stuff, there is something of a learning curve with ProCreate. I’d say it won’t completely replace green and brown stuff, and I know of professional sculptors who don’t much like it, but it is a welcome addition to the inventory.

EPOXY CLAYS

Milliput Standard Yellow-Grey
If miniature hobbyists have heard of only two types of putty, this will probably be one of them, and seems to be the one most try after green stuff (or indeed before it). The Milliput Company manufactures it, appropriately enough. It’s packaged as two 2oz/56.7g individually bagged bars – pale yellow and grey – in a small box, and is one of the cheapest putties, by weight.
Milliput lacks memory, making it useful for sharp details. However, it can be stiff in larger amounts. Its solubility makes it quite easy to smooth, but can cause a few problems with small details if water is used for lubrication. It also smells strongly, and is the only sculpting medium I've seen with a hazard symbol on the packaging (irritant). Despite it's popularity it has a reputation of being hard on unprotected skin.
Fully cured, it’s very hard but easily dry sculpted, particularly when carved.
I haven’t tried Milliput Black, Terracotta or Silver-Grey (yet), and I’m not sure how different they are from Yellow-Grey. I prefer Milliput Superfine White to Yellow-Grey. It is indeed very fine, and a little more elastic than Yellow-Grey. It can be sculpted very smooth, or polished with Wet And Dry sandpaper after curing – after which it looks a lot like ceramic (it was developed for repairs to ceramic objects) or white styrene. In my opinion it’s biggest disadvantage is that it’s very white, which might affect the visibility of small details while sculpting. I would imagine adding a little Milliput Black would darken it some, without affecting its properties too much.
Update: it seems like Luca Zampriolo does just that.
One of the unmixed parts of Milliput can develop a 'rind' when stored for some time. I've seen recommendations to cut this off and discard it, but I haven't had many problems mixing it normally.

Apoxie Sculpt
Manufactured by Aves Studio, packaged with each part in a separate tub, and available in a range of weights and colours. It can be good value in larger quantities. I’d recommend the lighter and more neutral colours for miniatures: the better to see detail with.
The putty can be sticky during mixing, but is less so when fully mixed. It’s possibly the least sticky of putties in this list. It behaves a little like Milliput Yellow-Grey, but is quite a bit softer. It’s less water-soluble – somewhere between Milliput and ProCreate. It also has a low memory, although I think the softness and solubility can make it initially too fragile for sculpting fine details. A browse of the Aves site shows that it’s primarily intended for sculptures and figurines in much larger scales than 28mm miniatures.
Apoxie Sculpt has a slight waxy feel without being greasy. The waxlike quality increases as it cures, making it easier and smoother to sculpt in my opinion, and holds stronger fine details. This helps to make it one of my favourite media on this list.
Cured, it’s strong and hard; maybe a little less than Milliput. The waxy quality is also noticeable when dry sculpting, which may make it a little less friable than Milliput.
Like Milliput, the unmixed Part B can develop a discoloured rind over time. Again, this can be a little stiff, but I've had no problems during or after mixing.

MIXING DIFFERENT TYPES OF PUTTY

This is where it gets interesting. I had to struggle to remember some of the properties of the putties in the list, since I rarely use them straight these days. Unfortunately it’s difficult to describe, particularly when mixing three or even four putties! The best thing to do might be to experiment and mix different putties in different ratios for yourself.
I’ve heard from some people who like mixing different parts of different putties, but it seems like waste to my obsessive mind. What do you do with hardener A and resin B if you’ve used up all of hardener B and resin A, and a mix of the first two isn’t as useful?
In general, different types of putty are mixed to combine the useful properties. In my experience it also reduces the effects of the worse properties. It also helps to make more expensive putties go further.

One of the most popular mixes is green stuff with brown stuff, usually less of the latter, used by some excellent professional sculptors. It reduces the stiffness and memory of green stuff, making smoothing easier and allowing sharper details.

Mixing an elastic putty with an epoxy clay is common too. The cheaper clays are useful for bulking out the elastic putties, often for understructure, while the elastic putty takes the edge off the solubility and inelasticity.

I’ve heard that mixing epoxy putty with polymer clay creates a hard-curing mix and prevents the need to bake the clay. I’ve had no experience with this, and I’m not sure how well the mix would work, but rest assured I’d find out for a future version of this article.

NOTES ON SCULPTING

When people post those new threads, curious about learning to sculpt, I always think the best answer would be the same as how to get to Carnegie Hall – practise! Practise, reference and work. Blood sweat and tears.

It's like learning to draw - step-by-step tutorials and guides can be helpful for tricks and techniques, but they aren’t a substitute for knowledge and skill. If you start sculpting seriously, you're going to have to look closely at things like anatomy, clothes, weapons, and proportions. You’ll need to gather and study your references, inspirations and influences. You’ll need to mess about and practise with the putty until you start to understand it and it starts to do what you want (I use the word 'start' deliberately). And you’ll need to put the work in.
Like Akira once said to Bart Simpson: "First you must fill your head with knowledge. Then you can hit bricks with it."

I may have been discouraging with that. It doesn’t have to be a chore, depending on how you approach it; although don't be fooled that you just need to glance at a tutorial or pick up a wax carver for the first time, and then sculpt like Tom Meier.

LINKS:

1listsculpting Yahoogroup.
Putty-n-paint. A tutorial.
Ebob miniatures. Some tutorials and a forum section.
Prophet Miniatures. More tutorials and forums. Beware his sense of humour.
The Slave Pit section of The Forum of Doom. A personal bias. Contains a much bigger list of links.
Reaper miniatures. A forum section, and a couple of useful articles in 'The Craft' section.
3D & Sculpture board on the Conceptart forums. It tends towards more larger-scale sculptures (and digital 3D), though that shouldn't matter much, and a few gaming miniatures turn up there too.