The sea-sponge is simply a coarse-grained sponge used to provide texture. Again, with the size of a mini, the grain is a bit too coarse to make a proper marbling.
I've been told the foam padding included with many minis works well for this sort of thing.
It just... didn't work out. I painted the Wych with a base colour, then applied the black wash. Some of the details became more pronounced, but the base colour became too dark. So, I tried to brighten it by re-painting most of the areas areas with the base colour again... but that destroyed the shading.
When using washes, you have to take into account the shading when choosing your base color: pick something a bit brighter than you want to end with. You can also thin down the wash a bit with some water.
I also tried highlighting: Wyches have these bits of plate armour I thought I could paint that way. So, I painted the armour with a darker metallic colour and tried highlighting the edges with a lighter one... but I'm so imprecise that I actually covered all of the darker colour.
Brush control, and also using good brushes. Note that the sharpness of the tip is more important than brush size when doing small details.
I also tried shading the hair, but it didn't work out too well, either. Somehow, the red wash I used for hair didn't enter too many of the crevices in the hairstyle, so not much of shading was done. I tried to add some more shades but painting some of the crevices with a darker shade of red with a detail brush, but the results are so-so. Hm
I'm not sure exactly what went wrong there, but my initial impression is that the wash was put on too thin/dried too quickly. It doesn't look like it pooled much at all.
No advise on shading, people? I'm going to have two free weeks now, so I'd like to come back to painting...
Not sure how much advice you want; Dhi is a far more skilled painter than I am. But I've found a few techniques that work well, and simply, to achieve decent results.
Breaking down by colors:
All the flesh is a simple base coat/wash; the key here was finding a really pale skin tone that looked bad in the bottle but doesn't look too dark after a wash. You can compare the skin of the characters with the decapitated head hanging from the right hip of the right guard; the only difference was swapping a thinned brown wash (agrax earthshade by GW) to give more pallor and less healthy ruddiness.
Zerkova's (the central figure) browns are two separate colors, P3 bootstrap brown and p3 gun corps brown, alternating from boots/pants/corset/bustier. I applied a brown/black wash (custom, but I believe very closely based on Secret Weapon's Armor Wash). That outlined all the detail and brought the colors together. I used multiple coats of wash in a few places to build up some shading, and returned to some highly thinned original colors for sparse highlights.
The metal is p3 thamar black base with a dry brush of p3 pig iron and a highlight of brighter silver (basically just a few touches on the most raised portions; I typically just dry brush a line down to the top of an arm/helm/weapon/etc). A little bit of p3 armor wash; I usually just apply that when my dry brushing is too heavy. Dry brushed metals are definitely something I suggest as a first step: it's very simple but adds lots of visual complexity. Inks or non-metallic metals look better, but anything is better than solid metallic base coat.
The fur is a mix of washes and drybrushing; I used p3 frostbite (a light blue/grey) for a mid tone, applied p3 armor wash for the deeper shadows, then dry brushed p3 morrow white for the highlights; the last one is actually used very sparingly, but it's so bright it's all you really read for color.
Over the last year I've been working on two brush blending, which does require some skill but makes for some striking effects that I really like. The red is Vallejo Gory Red as a base, mixed with a bit of p3 thamar black for a darker shade, then some more for a deep shade; I finished with some bright red (GW - maybe scarlet suns?) for a couple small highlights (top of the cap, her belt). I used armor wash to enhance a couple key details: the pocket on her left and the frogging down the front of her jacket.
The blue is successive dry brushed highlights (p3 meridian blue, arcane blue, arcane/morrow white, an a final touch of morrow white). I wanted to do some object source lighting but didn't feel confident enough - I need to get some junk models to practice on.
Some of my practice models, using two brush blending to create effects. 2bb involves laying down a base coat, then using one brush to paint a line, then a second brush - nearly clean, but wet - to smooth the edge out into a fade. This gave the two-tone cloaks, the three-tone swords (I mixed some vallejo metallic medium into the colors), and the light-glare look on the quiver.
2bb used to shade a light orange with a dark red.
Shading whites and blacks are notoriously difficult; this is a practice model for white after taking a class. His entire jacket is a mix of p3 gun corps brown and morrow white, with no pure versions of either. Washes only on the leather and rope.
The brown bottom of the coat combined 2bb (darkening from top to bottom) and washes (to pick out the details and edges).
So, back to your stuff: use washes, but plan for them. Your clothing didn't shade well because there's too little contrast between the wash and the paint color; that's fine if you're adding more highlights, not so good if you aren't.
That goes for the rest of your colors, too: you need another color in your palette that will work with your red to make easily identifiable shapes, rather than a formless monotone (a brighter gold rather than a bronze? switch to a different hair color?)
As mentioned, thin your paints just a bit. They will flow better, requiring less pressure on the brush and therefore a sharper point and better control and detail.
Regarding thinning the paints - hm, how much water is "little"?
I painted a new Sister today... I tried doing the shading again. It... came out better this time around, I think. Overall, I'm quite pleased with how the mini worked out.
The best description I've seen is to try for the consistency of milk. It should hold some form, but should flow readily and easily over the surface. Watercolor is bad.
And post the new mini!!!