Sorry for bumping this old post but it's what came up in the search results.
I just did the "Siegel Test" to confirm whether the 'veg-tan' leather I bought in Morocco was really veg-tan or not.
I have 3 different hides. With 2 of them, the samples immediately curled up and stayed curled which seems to confirm they're veg-tan.
With the 3rd hide, the samples (I tried a couple) immediately curled up but then straightened back out after being in the water for 5+ seconds?
I tried the burn test and the hides acted the same (no green ember I could see and they didn't burn very well, though the hide that 're-straightened' seemed to bubble out more liquid). The burned ends appear to scratch black (rather than green) on paper once burned.
The hides were all dyed through already and seem to absorb water well.
I think it's all veg-tan but I still feel uncertain - any other tests I can do? I won't be selling anything from these hides but I'd still like to know for sure what I'm working with!