I don't know which of the substances is responsible for what, but I'll
find out (this can take some time). I need only very few aggressive
chemicals and these only rarely, so I've been happy with my gloves and
mask and didn't make it my job to find out all about it.
As concentration for decorated paper making in general and marbling in
particular is far lower than for tanning I suspect there is no
immediate danger as long as you behave carefully. Sneezing fits and
prickling hands are certainly a signal, though, even when there are
lots of people never troubled by anything of the kind.