Color Changelings and Scott R190 to R194

Examples of Scott R190 showing color changeling progression. Stamp #1 is a normal stamp for reference. Stamp #s  2 & 4 are unused with original gum.

The post from October 9 explored fugitive ink on R183.  The unusual quality of that ink returned my attention to the R190 to R194 series of dollar values, which also seem to have an unusual type of ink, but unlike R183, there is no term or explanation like "fugitive" to explain this quality.  To the casual eye, these stamps were printed in green, with a black ornamental overprint corresponding to the value of the stamp.  Underlying the overprint, and not always noticed by the casual observer, is a small square of varnish (Scott notes that the varnish is on "some" stamps), added to show evidence of cancel "washing" -- the varnish is water soluble and washes off, taking with it the center of the ornamental overprint as well as any overlaying cancel.  

The green R190-R194 set of documentary dollar values is less common than the other sets as they were issued only months before the expiration of the tax period.  Production required three passes through the presses to create the final product - from original stamp impression to varnish to overprint/surcharge.

Occasionally a collector of these stamps may come across a color changeling -- a stamp in which the green has begun to change, and in some extreme cases change to a color that nearly matches the so-called "gray" color of the R184 to R189 series of stamps (the color of these stamps is a warm, sepia-like tone, not a cold gray in any way). An unused copy of R191 demonstrates this phenomenon (stamp #7 below):

The back of the stamp is marked in pencil by a previous collector as a copy of R185 with an R191 overprint.  The collection that it came from (I believe a different collector than the one that wrote the pencil note on the back of the stamp) also had a note from the collector on the side as an R185 with an error.  The color change on this stamp is extreme and seems rare according to my limited experience.  But the ink changeling phenomenon on these stamps exists, is capable of fooling relatively advanced collectors, and doesn't seem to have a clear explanation by my limited research.  More common are stamps that show lesser hints of color change, like those in examples 2-5 above.

I've never seen ink change like this on any other US issues, revenue or postage.  What is certainly unique about these stamps among US issues is the varnish square.  Richard Friedberg figures that the varnish is somehow responsible for the color changes, and it might have been, but the evidence doesn't lend itself neatly to thinking that varnish contact made the difference.  Consider stamps 3 and 4 below, where the stamps remain somewhat green closer to the varnish.  And, if the varnish was the cause of a change like that in stamp #7 below, why don't we see more of these changelings?

Another question is the timing of the color changes.  Did the changeling occur soon after printing?  I discount washing as a cause since some of the changelings I possess are unused stamps.  I've often wondered whether or not I've got slow changes happening to these stamps as they sit in my collection.  But I haven't noticed any color changes in the years that I've held some of them.  

Examples of Scott R191 showing color changeling progression. Stamp #1 is a normal stamp for reference.  Stamp #s 5 & 7 are unused with original gum.

Lastly, the $5 stamp, R192, provides an interesting opportunity to test varnish as a cause, as some of the stamps were issued without the varnish square or the overprint.

Examples of R192a, without overprint, and, apparently, without a varnish square. The left stamp is normal and provided for reference.  The right stamp is a color changeling.

The R192a on the right never had varnish applied.  Yet its color is clearly yellowing like many of the examples of R190 and R191 above.  In this case the explanation must involve the nature of the green ink itself.  The knowledge is likely long-gone from the BEP regarding the ink on these stamps.  But I suspect the right sort of chemist could help tell us what is happening.

I have a couple of non-changeling related questions, both involving how Scott lists these issues:  

• Scott refers to these overprints as surcharges, though the overprint does not revalue the stamp.  Why does Scott call these surcharges?
• In the "Warning" section below the image of R190 in the catalog, Scott tells us that the varnish was only applied to some stamps.  This needs to be unpacked a bit doesn't it?  First, most stamps appear to have the varnish, not "some".  Second, if cut cancels are sublisted for the 1898 dollar values, why isn't the presence of a clear overprint on used copies of R190-R194 sublisted?  And why isn't the presence of varnish sublisted?  I recognize that dealers and collectors don't seem to discriminate here and that is almost certainly the reason that varnish presence isn't listed.  But even without collector interest, the varnish clearly has an effect on these stamps, certainly with regard to how used, soaked stamps appear.  Used copies that have been soaked but retain the overprint are much more collectable to me, a bit like the lack of a cut cancel on these stamps.