AlexW wrote:

Yes ... but how do you identify each substance *reliably* - genuine
question. This seems a fairly important point.

People experienced in this will have a good chance of knowing what it is
by the situation they find it in, the material in question, age of the
building etc. Otherwise, and in case of doubt, you have to get it
analysed. Some local authorities do this, or you can use a private
analyst.

--
Holly, in France
Holiday Home in Dordogne
http://la-plaine.chez.tiscali.fr/