Until now.
For various reasons, being away and nursing a hurt foot after a long walk while on holiday, I'd not played with them for a good few weeks but got them out this morning. One was fine and still a thick goo with rolls off the skin pleasantly... but the other (the older of the batches, I think) has deteriorated into a slimy gooey mess more akin to slime. It's viscous, like a huge vat of brown snot-cum-glue, and it gets everywhere, is a real pain to clean up (it leaked over one side as i was getting out of the drawer it's hidden in) and has taken me most of my time before work just clearing up the drips, dribbles and vulgar colour splats through the kitchen after I discovered what had happened...
I assumed that the goo was probably starch-based or some similar gel agent, and I suppose stuff like this has a limited life, although I had built up this first batch over a period of months with no visible deterioration. But is this usual? And what kind of life can I expect the other to have (although admittedly, that's all fairly recent, and will hopefully not deteriorate for weeks or months yet!).
Which also leads me to ask, does the MPV Bleck 'deteriorate, and how the f**k do you get rid of it!?
I now have a tub of slimy goo that won't even wash off easily so I'm loathed to put my foot in it, now matter how wonder that might feel squishing between my toes, but once you've filmed your scenes in Bleck.. what then!? 
You've got more than a bathful! Does yours keep?
