I had been using Army Painter resin “dip” to shade models, as will have been seen in the Orc posting extravaganza over recent weeks. Since then I have moved on to their ink version.
I have found that each have their pro’s and cons.
The biggest things against the tinned resin dip are;
(1) the tin never seals very well and a large amount of the dip will dry up. I usually lost about a third of a can. As you can see in the photo below, you can end up with a massively thick layer of dried up dip, and what is below becomes unusable.
(2) The price. Considering how much was wasted, it was actually an expensive way to shade models.
(3) As it leaves a gloss finish, it is necessary to matt varnish the models to get rid of the shine.
(4) It is messy, smells and brushes need to be cleaned with white spirit.
But I do like the results from the resin dip, the models come up very nicely.
Over the last year or so I have been using the ink version of the Army Painter. As this comes in small bottles, it only costs a couple of quid at a time, it is water based, has a matt finish and does not go off. The finished results may not be quite as good, but it is much easier to work with. So I will be sticking with the Army Painter Dark Tone ink for the foreseeable future.
A loft full of lead 
Thank you for sharing your experience. Good to know that it solidifies during its lifetime. Did you consider filling it into an airtight container?
I tried all sorts of things, decanting some into other container, but then still having the rest in the can go off. I made strenuous efforts to keep the can lid clean, I never shook the can, I would stir it carefully.