I've put this in my Nurgle 101 tutorial at RelicNews, but thought I'd put it here for the Heresy crowd as well...
Here's something I've been asked for by quite a few people here (and elsewhere) - a tutorial on how to do the rotting skin and guts that seem to have become a bit of a speciality of mine
First off, here's the torso & legs that will be the basis for this conversion:
The first stage is to add a piece of green stuff that will serve as the 'foundation' for the final shredded guts; use your judgement to tell you how big of a piece of GS you want to use for this...
...I usually give this base-piece a sort of 'generic flesh' type of texture; at least some of this will end up being hidden as things progress but that doesn't really matter. Remember to have it protrude a bit from the torso for that authentically Nurgly pot-bellied look, don't leave it sitting flat to the torso.
The next step is to add guts, which I do by rolling variously-sized tubes of GS then attaching them to the background flesh...
...the more you can weave these together, the better. Actual entrails & intestines aren't neat and even, they're a chaotic mass of tubing, so try and get this feel with the GS; I find that making and interweaving tubes of GS like this to produce convicing-looking guts is really addictive
The side view here shows what I mean about having it protrude a bit from the body, this gives the finished area of the model a lot more depth.
Now, the tricky bit - making skin. In the end, the only really realistic-looking way I've found to do skin with GS is to basically make a literally skin-thick layer of the stuff and stick that on the appropriate area of the model. The best way I've found to do this so far is to take a small piece of GS, squeeze it flat then tease out one edge with a pair of tweezers till it's almost translucent...
...keep the tweezers wet so the GS doesn't stick to them, and gently pull at one edge of the flattened piece of GS till you get it looking about right. This is very much a 'feel' thing, but with a few tries you can start to get the right kind of thickness happening.
Now apply this to the model gently
; a piece of GS this thin will tear easily and also try to stick to anything more solid than an air molecule if you give it half a chance, so you have to be pretty careful at this stage...
...once you've got it in about the right place, start to work the non-ragged edge in carefully
till it's attached reasonably firmly to the model; then you can start to move the ragged edge around to where you want it. Do it this way so the piece is anchored to the model, as it's so thin and light overall that even breathing out too hard can move it out of place.
Then basically just work the skin piece into the model till everything's where you want it. I leave the skin sitting just above the guts rather than being stuck down onto them, this lets you move it around for purposes of correct positioning (which you really wouldn't be able to do with GS this thin if it was attached to the flesh underneath). GS this thin will
move and deform as you work with it, so be prepared to adapt to what the material does as it's applied; this isn't really a problem, though, since you're going for an overtly organic and uneven effect anyway. You can add other pieces to it, as with the left-side piece you can see here:
...in fact I'd recommend doing something like a belly (as in this example) in about 3 main pieces, as this technique is so dependent on the behaviour of gossamer-thin GS that you really wouldn't want to try and do it in one whole piece. Joining together pieces of GS this thin is pretty tricky, but do-able with some practice; I use the wetted tip of a cocktail stick to very
gently smooth them together till they adhere to each other properly. If the GS tears as you apply it, don't worry, just make that part of the final look; in fact, I usually count on at least a few such little rips and tears appearing, as that just adds to the effect
Et voilà! Putrid entrails à la mode
I've included the angled shot from overhead to show the effect of having the guts stick out a little from the torso; this gives the model a lot more 'weight' visually to my eye, and the overall look of the torn skin with layers of stuff behind it gives an effect of real depth and three-dimensionality to a model that I really, really like. It's also great when it comes time to paint it, as you have real
layers and contours to work with.
Here's the same effect on a couple of other Plague Marines:
...and some detail shots of the Possessed Terminator I made for the conversion competition at RelicNews
to show how you can have several different areas of the same effect on one model:
As always, I hope this was useful to people.