Question to experienced people

[ФАИв]

Several years ago, when the question arose about the time of writing a work (according to the seller, the work was more than 30 years), an artist friend of mine advised me very carefully, in the invisible part of the regular sewing needle poked pasty place of painting. If the paint is soft - that work has been written recently, if the firm as a rock, then over time. Interested in your opinion, is valid whether such "express - analysis" under the following conditions:
1. Painting technique allows a manipulation
2. Do you have permission from the owner, or there are conditions to do so.
3.Proyavlenie maximum caution in relation to work. (Although this in itself is an axiom)
4.Nu and understand that this does not negate all the standard procedures to verify the authenticity of what you have set.

And so, this raises the question to the experts: If the work is "washed" and varnish - old painting softens? What is the technology of cleaning dust and dirt that inevitably leads to a softening of oil paint?