I usually take samples that I need to be identified to the State University. UNC loves to do this kind of stuff, expecially for homeowners. You just have to find the right guy to talk to.
If you have a univ. in your area take your samples there. Another place to take samples to is the State and/or Federal EPA. They have some very significant labs.
Go to your (or call him/her) id your representatives in the legislature. They would trip on the opportunity to help a homeowner with his projects. Just be sure to tell him/her that you are a constituant.
Once you know what type material it is you're looking at you can then decide what method to use to remove it.
However, Before you go through all of the time, hassel and expence of looking for a lab try out a few things.
Try different types of alcohol. Isopropyl, rubbing etc. Xylene and some of the other chemicals you can find at hardware stores such as Lowe's or HomeDepot. Your hairdryer Water (probably wont work Chisels........hehehehe
The first thing you should do whenever you are working on your home is to use the least effecting method first.
By this I mean to use water first. then work your way up the damage scale form there.
water, alcohol, chemicals, chisels etc
Now, if the glue is still plyable I would first try to use the chisel method. But I would not try to actually chisel it with a hammer. I would use a putty knife and see if I could pry it loose.
When you finally have the glue off you'll most likely have a few new problems.
One, if you use chemicals to remove it, you 'll have a residue of glue and chemicals you'll need to remove. Contact the menufacturer of the chemical and ask them for them method of reversing the chemical. Some chemicals require you to use certain other chemicals to reverse.
If you don't reverse the chemicals then the new plaster bonding agents may not adhere to the chemicals and your hard spent time restoring your walls will fail.