I hope to get an answer on this forum. Cannot find explanation to my dilemma anywhere so far.
Some Bolivian souvenir sheets from the 80's are printed by La Papelera SA (Bolivian company) and some by Lito. Nacional-Porto-Portugal (Portugese company).
The ones printed by La Papelera SA have perfect reverses with perfect gum. The gum has very-very light tinge of yellow and souvenir sheets are bending slightly upwards on flat surface.
The ones printed by Lito. Nacional-Porto-Portugal have snow-white gum which has numerous superficial scratches - they are tiny or bigger. Those scratches are seen under some angle to the light. No obvious fingerprints. Souvenir sheets are staying flat on flat surface.
I examined a few dozens of those souvenir sheets. They come from various sources. It never happened that the ones from La Papelera SA had any marks on the reverses, but the ones from Lito. Nacional-Porto-Portugal always had. It cannot be a coincidence - I cannot be possibly so unlucky.
I noticed the same scratch marks on some souvenir sheets from Paragway, however there is no printing company name on the Paraguayan items.
Those scratch marks are regarded as defects by more concerned collectors.
My question: are those scrathes caused by the production process itself (the souvenir sheets have them already when they leave the printing facility), or the gum material is so prone to damage that a slight movement against any surface, including against stamp mounts, results in those ugly marks?
I would appreciate if anybody could through some light on this problem.
I am referring to all those shiny marks on my pictures: they are different in size and looks, sometimes linear, sometimes looking like I were rubbing the gum (I was not, of course), or scratching them with brush (I was not neither). All blocks and many stamps printed by Lito. Nacional-Porto-Portugal.
Adam - I do see what you are talking about. I think that it should be considered as natural by experienced collectors. I collect Russia now and the quality of many of the stamps and souvenir sheets from the 1930's through the 1950's as far as gum and paper leaves much to be desired and it did even if you bought them brand new back then. It is expected. The gum on some of the 1930's sets is notorious for being streaky, bubbly and splotchy but that is the original condition and so it is acceptable to collectors that know what to expect.
I think that there is a lack of understanding amongst novice collectors of what is normal for condition. We collect pieces of paper that are often many decades old and were mass produced as utilitarian disposable items.
The essence of your observations is here: "(..) it is acceptable to collectors that know what to expect. I think that there is a lack of understanding amongst novice collectors of what is normal for condition."
I come across collectors who have their own set of ideas of what the "philatelic item of good quality" is. Those collectors create a list of parameters unknown even to experts in the field (seriously), and in spite of what for example Stanley Gibbons guys have to say on their catalogues' introductory pages. It is a bit like talking about music to an audiophile, who elaborates on some graphs instead of really enjoying the piece.
You are right: it comes from experience, which establishes reasonable expectations.