I love it. I'm going to borrow some of those ideas for basing my Plaguebearers. Are you using a specialty product for the goo or is it a paint added to a medium?
It's fairly straightforward. For the goo, I airbrushed a base layer of caliban green, then moot green (leaving the caliban at the edges), then moot green mixed with about 25% flash gitz yellow. as a final highlight in the middle. This could have been hand painted. The clever bit is I then put on a thin layer of greenstuffworld 'toxic effect' UV resin. This gives the liquid effect up the side of the stone (which really sells it, I think), the glossiness, and smoothes out the underlying paint. The "toxic effect" is basically just their clear UV resin with some lime green fluor paint in it. It's pretty translucent, thus the moot green layer underneath to give it something to tint.
Next time, I'm going to add some greenstuff hemispheres as bubbles before priming.
The big advantage of the UV resin in that you can set it in 120 seconds with a UV light - I picked up the UV torch from greenstuff world too. I didn't need to tape up the edges, as it's fairly gooey, but settles level easily. Given it's only a thin layer, you could easily get a similar effect with any water-effect resin and a bit of lime-green ink, I think. The fluorescent ink does make it have a tiny bit of a glow under bright light, as you can see in the final pic. Looks properly radioactive IMO!
The stone is just 1.5mm cork sheet cut roughly to shape (two layers), primed grey, covered with astrogranite, light wash of nuln oil, then drybrushed with dawnstone and grey seer. I did this before the goo, so the airbrush naturally oversprayed a bit onto the stone (you can see the green tinge on the closeup), and I evened it out with a final drybrush of moot green round the goo-facing edges, and matt varnish to protect (before goo).
edit: Not easy to take a pic of how it looks under UV light, but

Edited by Arkhanist, 15 July 2020 - 01:23 PM.