Develop Please doubts

[OlegTsi]

I think I see traces of paper, which was sealed around the perimeter of the back of the frame. If so, it protected the back of the picture of the impact of external factors. The dust may not penetrate the front or the back side. Himself a frame (if it is pine) has acquired a natural reddish tint. And all of equal importance is the conservation factor (constant relative humidity and temperature), and the degree of care for the picture. Those who have spent today 100 thousand euros, I think, were able to verify the authenticity of the paintings and, accordingly, its age.
For more conclusive findings would have to watch the stretcher and canvas in hand.