Background: [the company] makes a heavily-pigmented, oil-based mixture that is not typically sold in shops but directly to end user(s).
The mixture is predominantly vegetable oil(s), natural waxes (e.g. beeswax/rice bran wax/other), mineral pigments (approx 1/3 of mixture), some emulsifiers to aid wash off (polysorbate 80 and oleyl alcohol) and methylparaben as preservative.
Issue: Have noticed 'leaching' of something oily from one of the colours of a batch that has been in stock for circa 18mo. To me there is a slightly stronger, waxy/oily odour than normal but not overwhelming or particularly rancid. Under the 'leached' oil-stuffs the top layer is now spongy and not spreadable. The top layer is not combinable with the leached oil-stuffs either at room temp or under heat (as per manufacturing of product). The leached oil-stuffs is stringy, tacky, sticky unlike any of the raw materials or combinations thereof.
Question: Am I on the right lines that it is spoiling in this one instance? There are other colours that have not exhibited this. All colours feature mineral pigments - the one differential is that the colour with issue features a FCF lake pigment also, in small quantities. I have used this in the same base but with additional pigments without issue. We have an accelerated stability PAO of 6mo but the product has not been in our repertoire for particularly long (circa 24mo).
I have attempted recombination/reconstitution without success (remains caky/lumpy with basic stirring under heat, unlike unspoiled product which melts quickly and homogeneously). Have also tried retaining at temperature (35°C+ for circa 2 hours) to try and accelerate leaching. Removing leached oil-stuffs and holding at temperature shows no leaching/sweating of product. Correct consistency product shows light leaching/sweating at temperature. Removal of top skin of spoiled product shows light leaching/sweating consistent with unspoiled product.
I'm inclined to think it's not a stability (of mixture) issue given that other colours have remained correct in storage.