Henk, do you have the trouble getting formaldehyde in Europe/Netherlands, etc. that we have in the US ? I suspect it was because it was (allegedly anyway) an ingredient in making crack or some other illegal intoxicant, but it was ixnayed everywhere in the US except by doctor's prescription .... apparently for athlete's foot, or like that.
I myself was delighted to switch to glyoxal for hardening gum size, because, even used outdoors it was deadly with a class, & almost as deadly indoors by myself at home in winter. So I got out of the habit... However, there are some things it still does best and now that the remains of my last bottle have evaporated (probably into the lungs of this household and the neighbors), I expect to use my influence to get some more. (Tho folks who have some should be sure to check that it's tightly sealed, because it's apparently very volatile.
Meanwhile, what I meant to ask in this rambling message is, what concentration formaldehyde is that?