Prince Edward Island - Bud's Big Blue

Scott #6, blue

Bud's Big Blue

Bud's Observations

All Prince Edward Island (PEI) stamps bear the image of Queen Victoria, some resembling the artists’ original depictions, others not so much. Early British colonial postage often slumps toward the dowdy. A. A. Bartlett, an early advocate of PEI stamps, penned the improbable hope “that these wretched little things, though far removed from being ‘things of beauty,’ may still become ‘a joy forever’ to many a philatelic album.”(1) In 1895, catalog values for his PEI collection fell far short of those enjoyed by New Brunswick and Newfoundland fanciers.

As with other colonies, PEI relied on the familiar profile on the British “penny black” for its first stamps. This can be traced to a sketch drawn by Henry Corbould based on medal of Princess Victoria designed by William Wyon. The medal commemorates Victoria’s first visit to London after becoming Queen (1837).

Medal by William Wyon, 1837

PEI added a curious burelage to this design. It appears to the naked eye as wavy chain links, but magnification shows a network of lines and dots (on Scott #s 1-8 only, although others have similar). Most colonies use fine parallel lines or solid backgrounds, as did PEI for some later issues.

Magnification of Scott #6 

A more stunning image resulted from Samuel Cousin’s engraving of Alfred Chalon’s portrait, which was printed and distributed on the day of Victoria’s coronation.

Queen Victoria in coronation robes by Alfred Chalon

This full-faced image, used in several colonies, is to me more attractive than the alternatives. Sadly, PEI tried it only once (Scott #10). The “Stg” and “Cy” denominations at the bottom of the stamp refer to respectively to British sterling and PEI’s considerably devalued currency – two prices, depending on whatever cash was in the purchaser’s pocket.

As adapted by Samuel Cousins, Scott #10, brown

When the currency changed from pence to cents (1872), the queen’s philatelic visage became less flattering, although she gains a ribbon for her hair. This final PEI image is based on the British 1860 “bun penny,” a bronze coin, also designed by William Wyon. BB provides five spaces for these last PEI stamps under the rubric “1861-68”, which should read “1861-72”.

1860 “Bun Penny”, Wyon

The “bun penny” image was adapted, unsuccessfully in my opinion, for many colonial stamps – note the pouting lips and bulging eye not obvious on the coin.

Scott #14, green

PEI joined the Canadian Confederation in 1873, thereby ending its philatelic history as well as its options of it becoming a discrete British-related dominion or a state within the USA.

Four more brief comments.

Over a century after A. A. Bartlett worried about poor catalog values for PEI stamps, collectors of his “wretched little things” now find their PEIs have CVs that compare favorably with those of other maritime colonial stamps. Bartlett would feel vindicated.

In her day, Queen Victoria’s image appeared on more stamps than anyone else’s. BB provides the evidence, should you care to make a count. Now her great-great granddaughter holds that record. 

Isle of Man, Scott #889, multi, 3 Victorias, 1 Elizabeth

All my PEIs showing below are mint, owing probably to the large number of unused stamps remaindered after PEI joined the Dominion of Canada. At the time, they were sold at a small fraction of their face value and the more common of them took years to deplete.

A final comment. The best lobster meal, perhaps the best meal of any sort, we ever had away from home was thanks to PEI lobsters. We went to the wharf to pick them out when the dory returned. Husky critters, snapping fresh from the traps. Then our B&B host prepared them and served them with fresh asparagus and lettuce, and an excellent chardonnay. Absolute serendipity. Unfortunately, no PEI stamps commemorate these famous residents. 

Census: nine in BB spaces, three tip-ins.

(1) A. A. Bartlett, “Prince Edward Island Stamps”. The Stamp News (October 1895).

Jim's Observations

Anne of the Green Gables (1908) , a novel set in Victorian times on Prince Edward Island, forms for many, the first exposure to the people and landscape of this small province, located in the Canadian Maritimes.

Big Blue '69 has Prince Edward Island on two lines of one page, shared with Penrhyn Island. There are nine spaces, or 56% coverage of the total stamp output. The page is located after Panama, and before Papua.

The 40s BB editions have the same coverage, but the page is located before Persia.

The coverage cannot be faulted, as any missing spaces are more expensive.

There are three stamp spaces in BB with CV $10+-$20+.

Except for the 1870 3/4 portrait queen which is engraved, all the other issue stamps are typographed. I admit I prefer engraved stamps for my "classics". I think they look better.

But the prices are right for these unused specimens- so I am not complaining much. 

Prince Edward Island Blog Post & BB Checklist

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Comments appreciated!

COGH 1858-64 Triangular Six Pence Varieties

1864 SG 20 (Sc 14) 6p Bright Mauve (Purple) 

DLR Printing

Into the Deep Blue

The Six Pence, like its fellow COGH Triangular siblings, was printed by Perkins Bacon (1858-63), and, on PB plates, by De La Rue (1864).

The Perkins Bacon era can be further divided into the slate-lilac (1862) or slate-purple (1863) on blued paper issues; and the 1855-58 deep rose lilac (1858) or pale rose lilac on white paper issues.

The DLR 1864 Six Pence is bright mauve (Scott says "purple").

(Note: SG color descriptions will be used primarily, although I will include Scott's description also.)

I should mention at the outset that Chris Dorn (Beryllium Guy) of The Stamp Forum helped significantly to clarify my thinking on these Six Pence stamps. Thanks Chris!

The best way to learn is to look at examples in my collection, so let's begin. 😎

Example 1

1862 SG 7c 6p slate-lilac/ blued paper 

(Sc 5b 6d grayish-lilac on bluish paper)

PB Printing

The slate-lilac colors of the 1862 issue are relatively easy to identify. This example to me has more "slate" than "lilac". The CV is a rather hefty $540.

Reverse- 1862 SG 7c 6p slate-lilac/ blued paper 

PB Printing

The other reason the PB slate-lilac (or slate-purple) stamps are more easily identified, is they are the only ones to have paper "more or less blued', seen here on the reverse. (For the other Six Pence stamp varieties, the paper is "white")

Example 2

1862 SG 7c 6p slate-lilac/ blued paper 

(Sc 5b 6d grayish-lilac on bluish paper)

PB Printing

Here is another "slate-lilac". To me, this stamp shows more "lilac" than "slate". Probable "fiscal" use.

Close-up: 1862 SG 7c 6p slate-lilac/ blued paper 

Could this stamp actually be the rare "purple" color (1863 SG 7d (Sc 5c) with a CV of $1200? Well, the "slate-lilac" can come in shades, so this is probably still within the "slate-lilac" group. And the "slate-purple" is rare. But it has a fiscal script of 1865, so possible (but not likely).

Reverse- 1862 SG 7c 6p slate-lilac/ blued paper 

The reverse only shows spotty bluing, but definitely there.

Example 3

1858 SG 7 6p pale rose-lilac/ white paper

(Sc 5 6d pale lilac); PB printing

Now we will look at the other major Six Pence PB grouping - the pale or deep rose-lilacs of 1855-58, on "white" paper.

This stamp appears to be a 1858 "pale rose-lilac". CV is $300.

The major problem for collectors of the "rose-lilacs" is the frequent fading of the stamp color, due to light exposure. This example is an exception: it shows decent detail and color.

Reverse- 1858 SG 7 6p pale rose-lilac/ white paper

Note the "white" paper. 

Example 4

SG 7b 6p deep rose-lilac/ white paper

(Sc 5a 6d rose lilac/ white paper)

PB Printing

This example has a deeper color, and is probably a "deep rose-lilac" variety. Again, decent detail with no apparent fading. CV is $400.

I should mention that the PB "deep rose-lilac" color can sometimes be confused with the 1864 DLR "bright mauve" (Scott "Purple"). But this stamp looks like a PB printing with more detail evident.

Reverse- SG 7b 6p deep rose-lilac/ white paper

The reverse shows "white paper".

Example 5

1858 SG 7 6p pale rose-lilac/ white paper

(Sc 5 6d pale lilac); PB printing

A local dealer had a cache of "Six Pence" stamps - six or seven of them. All of them were badly faded, except for this example. I was hoping this might be a DLR stamp, as I did not yet have one. But closer inspection shows some background detail, and the color is probably not "bright mauve". 

Reverse- 1858 SG 7 6p pale rose-lilac/ white paper

White paper- no evidence of bluing.

Example 6

1864 SG 20 (Sc 14) 6p Bright Mauve (Purple) 

DLR Printing

When I saw this stamp for sale at the APS site, I had high hopes this would turn out to be a DLR 1864 "bright mauve".  Notice the very poor detail in the background and the lack of detail with "Hope". 

I should mention, though, that Six Pence DLR stamps are not as commonly found compared to PB stamps. 

Reverse- 1864 SG 20 (Sc 14) 6p Bright Mauve (Purple) 

DLR Printing

"White" paper as one would expect. One can see the watermark.

Comparing a PB "rose-lilac" with a DLR "bright mauve".

I asked for a Cert. The APS uses two experts for APEX, and they have to agree. Four months later, I got the result: Indeed a DLR 1864 SG 20 (Sc 14) 6p Bright Mauve (Purple)! CV is $450.

Out of the Blue

The major problem with Six Pence stamps is finding a good specimen, as the "rose-lilacs"  are prone to fading. And then finding a genuine DLR Six pence is sometimes difficult. They are not that common, and the PB "deep rose-lilac" can be confused (and sold as) the DLR stamp.

Comments appreciated!

Penrhyn - Bud's Big Blue

Scott #s 62-63, 1974

Bud's Big Blue

Bud's Observations

Some 266 Polynesian Islanders live atop a “pie crust” reef that rests on a long-extinct volcano. Their 40-mile-long strip circles a 90 square mile lagoon (compare Oregon’s Crater Lake at 20 square miles). The Penrhyn Atoll, aka Tongareva, lies south of the equator and is the outermost part of the Cook Islands (see map in Scott #63, above). Total land area is 3.8 square miles. Its nearest neighbor is 220 miles to the southwest. Ships pass by rarely. Air transport is unscheduled and unpredictable.

Stamps were issued for Penrhyn Island two times in their history. From 1902 to 1920 stamps of New Zealand were overprinted for Penrhyn, followed by stamps like those of the Cook Islands but with “Penrhyn” inscribed, 1920 to 1932. In all, Scott list 31 major numbers while Stanley Gibbons counts 40. BB provides spaces for 19. 

Scott #8, blue with carmine overprint

Then, from 1973 to the present, Penrhyn stamps were again issued, this time with the additional inscription “Northern Cook Islands.” Recent issues have attracted a following of bird and fish topical collectors. Penrhyn Atoll has few terrestrial flora and fauna.

Scott #61

Remoteness and population decline have severely limited Penrhyn’s postal services. Today’s population is almost half what it was when the stamps in Big Blue were in use. Authentic cancellations, therefore, cost more than mint examples. Philatelically inspired cancels are commonly pinked on more populous islands.

Capt. James Cook, Scott #27, violet and black

My collection is entirely mint. There is no Penrhyn supplement page.

Census: 19 in BB spaces.

Jim's Observations

I suspect only philatelists, Pacific ocean yacht owners, and assiduous National Geographic readers are aware of Penrhyn Island. 😎

Penrhyn Blog Post & BB Checklist

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Comments appreciated!

COGH 1853-64 Four Pence Blues Triangulars: Treatment of Sulfuretted Stamps

1855-58 COGH SG 6 (Sc4b) deep blue/ white paper

Upper: Sulfuretted; Lower: Treated

Into the Deep Blue

I have some 40 Cape of Good Hope 1853-64 Triangular Four Pence Blues, and perhaps a third of them show some degree of sulfuretting. Yes- a lot. !! These ugly gray-greenish- brown spots can change the perceived color of the stamp.

I touched on the problem with this post...

COGH 1853-64 Four Pence Triangulars Part A

..where two stamps (Ex 8 & 9) showed evidence of sulfuretting. I also gave an explanation and details of my understanding of sulfuretting. 

As I would prefer, with this blog post, to just do a "show & tell" of some of the sulfuretted stamps in my collection, I will put the chemical explanation of "sulfuretting" at the end of this blog post, if the reader wishes to read it. (The explanations are still speculative, as I have found suggestive, but not definitive literature on the subject.)

Example 1

1855-58 SG6 (Sc4b) 4d deep blue/ white paper

Upper: Sulfuretted; Lower: Treated

One can see the sulfuretting discoloration most clearly by the feet of "Hope Seated", but there are other areas also. Would 3% Peroxide treatment work for this stamp to restore the original color? Most collectors are aware that orange or yellow stamps can show a degradation to brown due to sulfuretting. But it turns out the COGH 4d blue stamps with brown sulfuretted spots also can be treated!

After using the Stamp Smarter Weiss technique, the result is dramatic and stunning. The stamp is returned to the original blue color. Most of the dark spots are removed or significantly diminished.

Example 2

1855-58 SG6 (Sc4b) 4d deep blue/ white paper

Upper: Sulfuretted; Lower: Treated

The issue that is most affected in my collection are the Perkins Bacon  1855-58 SG6 (Sc4b) 4d deep blue/ white paper varieties, which are also the most common 4d blues in my collection. CV is $85-$90 (used), compared to $170-$375 for PB 1853 paper "more or less blued" specimens, and $135 for DLR 1863-64 specimens.

And there is another twist: the "deep blue" colors (SG6 (Sc4b) are more affected by sulfuretting than the "blue" colors (SG 6a (Sc 4)*. In fact, in the iconic Stevenson book (published 1953) on COGH Triangles, he states the deep blue 4ds are susceptible to "oxidation" (actually sulfuretting), turning an almost indigo color at times. That could explain the change in blue coloring within the stamp.

*What came first, the chicken or the egg? I noted that the conventional COGH literature states that the "deep blue" color is most susceptible to sulfuretting. But a stamp with sulfuretting will be perceived as having a darker blue hue. After treatment with Peroxide, the stamp invariably looks less "deep blue", and more "blue". (See for yourself with the examples presented here.)

Example 2 Reverse

Reverse Side: 1855-58 SG6 (Sc4b) 4d deep blue/ white paper

Upper: Sulfuretted; Lower: Treated

How does the Peroxide treatment affect the "white paper" reverse side of the 1855-58 SG6 (Sc4b) 4d deep blues?

Generally, it removes micro-debris and gum debris. (Caution: Immerse in Peroxide only on "used" stamps where one doesn't care about gum remnants. Don't immerse an "unused" stamp with intact gum - you will lose the gum.) 

And it can cause apparent "whitening" of the paper. (Recall that Peroxide can be a bleaching agent. This may be a function of how long the stamp is immersed in the Peroxide.) 

Actually, in my opinion, most of the "whitening" is because of removal of yellow gum debris. 

Still, I am quite conservative, and only immerse the stamp in Peroxide for 60 seconds, followed by a water bath, and then overnight drying and flattening in a stamp drying book.

Example 3

1855 SG 6a (Sc4 or 4e?) 4d blue / white paper (over-inked)

Upper: Sulfuretted; Lower: Treated

This stamp has some sulfuretting near the foot of "Hope Seated". This is cleared up with Peroxide treatment.

Now to my eyes, this stamp is more "blue" than "deep blue" after treatment. Perhaps this is a SG 6a 4d blue/ white paper? This interesting blue color, Scott wise, could be a Scott 4 4d blue/white paper, or possibly a Scott 4e "bright blue"?

Note the "engine-turned -background" around "Hope Seated" has little detail on this Perkins Bacon printed stamp? The term "wooly" is sometimes used for this condition, especially with De La Rue printed stamps. For the DLR stamps, it is thought that the DLR prepared paper and the DLR ink did not adhere well together, leaving pools and flakes of ink.

With the Perkins Bacon stamps (such as this one), the "wooly" feature is thought to be from over-inking - a different cause.

And, although most stamps that are sulfuretted are a "deep blue" color, this stamp is sulfuretted AND appears "blue" after treatment. Of interest, the sulfuretting is occurring on an over-inked "blue" stamp. Possible cause?

Example 4

1855 SG 6 (Sc 4b) 4d deep blue/white paper 

Upper: Sulfuretted; Lower: Treated

This specimen also shows sulfuretting by the foot of "Hope Seated, but other areas as well. The stamp is definitely improved with treatment.

Example 5

1855 SG 6 (Sc 4b) deep blue/ white paper (over-inked)

Upper: Sulfuretted; Lower: Treated

This stamp is not the best (diagonal crease, large obliterator cancel), but I show it to see if the reader can spot the sulfuretting.

Also the stamp has lack of detail in the engine-turned- background. But the color is wrong for a DLR issue (not an indigo color), so this is an over-inked PB specimen.

I should mention that I have not seen an example of a 4d blue DLR stamp that is sulfuretted. Perhaps the paper-ink DLR process has prevented that from occurring?

Note: The sulfuretting is found above "OD HO" of "GOOD HOPE".

Example 6

1855 SG 6 (Sc 4b) deep blue /white paper (a sharp specimen)

Upper: Sulfuretted; Lower: Treated

This is an interesting stamp. To my eyes, this stamp's color, although I labeled it "deep blue", does have some "blue" qualities after treatment. 

But most stamps that are found sulfuretted are "deep blue"*, and this stamp is clearly sulfuretted (most obvious between "Hope" and "OUR" of "FOUR).

*I'm actually beginning to wonder if the sulfuretting, which causes the stamp to assume a darker hue (perceived color), is the reason that conventional wisdom states that "deep blue" stamps are more susceptible to sulfuretting? Because, after treatment, and apparent restoration to the original color, the stamp doesn't really look "deep blue" anymore, but often more "blue".

Note the "engine-turned-background" is "sharp": the boomerang markings and dots are quite evident.

Example 7

1855 SG 6 (Sc 4b) 4d deep blue/ white paper (quite sharp)

Upper: Sulfuretted; Lower: Treated

Can you find the sulfuretting? I show this stamp because sometimes the cancel markings can be confused with sulfuretting. 

I think there is a patch between "Hope" and "R" of "FOUR".

I'm finding little reason to not use Peroxide treatment if one is suspicious of sulfuretting. It also helps to remove 160 years of debris and grime from the stamp. Still, it does go against my general approach of "leave well enough alone". 😎

Example 8

1855-58 SG6a (Sc 4 or 4e? ) 4d   blue/ white paper (over-inked)

Upper: Sulfuretted; Lower: Treated

The sulfuretting is extensive: major areas include around the feet of "Hope", and below "TAGE" of "POSTAGE". The areas are improved nicely with treatment, but leave a "blue" stamp that is over-inked (little detail in the engine-turned-background).

Most of my stamps that are sulfuretted are "deep blue". But this is now the 2nd stamp I have found which is "blue" to my eyes after treatment, sulfuretted, AND over-inked. It may be that  PB 4d stamps that are over-inked are more susceptible to sulfuretting?

Also, note the large perceived color difference in the stamp before and after treatment? I think that drives home the lesson that color of a stamp that is sulfuretted should not be assigned until the sulfuretting is removed.

Example 9

1855-58 SG6 (Sc 4b) 4d deep blue/white paper (over-inked)

Upper: Sulfuretted; Lower: Treated (Here for 10 minutes)

Now this stamp is interesting, and not in a good way. Note the essentially green color along the "Four pence" edge?  Could this be a color changeling (due to exposure to chemicals), or perhaps an especially egregious form of sulfuretting?

OK, I treated with Peroxide for 60 seconds. A 60 second immersion was not cutting it, so I extended the immersion to ten minutes.

And the result was.....No change.!! There was not one bit of difference.

I think we can safely say the stamp was subject to some sort of chemical change, not sulfuretting. (From my chemistry study days, when I see green, I think of copper compounds.)

Example 10  Reverse

Reverse Side: 1853 SG 4 (Sc 2) 4d deep blue/ slightly blued paper

Upper: Sulfuretted; Lower: Treated

OK, this stamp gives us a bit of mystery (primarily on the reverse). What is the brown discoloration? Is it sulfuretting or something else?

The stamp itself was identified as a 1853 SG 4 (Sc 2) 4d deep blue / slightly blued paper specimen. (One could perhaps argue that the paper bluing is extensive enough to call this a 1853 SG 2 (Sc 2a) 4d deep blue / deeply blued paper.) 

One has to be very cautious here, because there is a risk that the Peroxide treatment COULD diminish the paper bluing. After all, the reason Perkins Bacon added paper bluing was to make the ink  "singly fugitive" to organic solvents. If I can quote Chris Dorn of The Stamp Forum:  "It means that if one attempts to remove a cancellation by means of a solvent, that the ink will be affected in such a way as to show that the stamp has been tampered with". 

Certainly Benzene, as a solvent, might cause damage. But what about 3% H2O2 (97% H2O)? 

Right or wrong, I went ahead with the Peroxide treatment.

And success! The browning completely went away, leaving intact paper bluing, which appears to be not diminished in intensity. Yes!!!!

Example 10

1853 SG 4 (Sc 2) 4d deep blue/ slightly blued paper

Upper: Sulfuretted; Lower: Treated

There was also some sulfuretting on the face side of the paper blued stamp.

Close-up: 1853 SG 4 (Sc 2) 4d deep blue/ slightly blued paper

Upper: Sulfuretted; Lower: Treated

The close-up shows the sulfuretting (below the feet of "Hope"), and the removal with Peroxide treatment.

So what do we know now?

a) Sulfuretting can affect the 1853 PB 4d deep blue/ paper more or less blued specimens.

b) Treatment of the sulfuretting in this case caused no loss of paper bluing intensity. !!!

c) Most sulfuretted 4d stamps are of the PB 1855-58 4d deep blue/ white paper variety.

d) I am not aware of any sulfuretted 4d stamps that were printed by DLR (1863-64).

(Note: Caution on using H2O2 on blued paper specimens. Some very heavy hitter experts on COGH triangles do not advise this, as they are concerned it could remove bluing from the paper. But I tried it on the above blued Four Pence specimen that had sulfuretting, and there was no loss of bluing at all (and it removed the sulfuretting!). Nevertheless, I would advise treading softly in this area.)

Out of the Blue

I think I have shown and demonstrated that, for sulfuretted COGH 4d blues, treatment with Peroxide works very well to restore the original color, and removes grime and yellow gum debris. 

If the reader agrees, perhaps he/she can try it cautiously on one of their own sulfuretted COGH 4d blues? 😎

Appendix: The "chemistry" of Sulfuretting (Specifically for the COGH 4d blues)*

* Possible alternative explanation of Sulfuretting given in Part B below

Part A

I should mention at the outset that the following are my ideas, and ideas I gathered by reviewing the chemistry literature, of what is occurring chemically. I may be right or wrong in my conclusions. 😎

(The explanations are still speculative, as I have found suggestive, but not definitive literature on the subject.)

What is sulfuretting? 

When we use the term here for the COGH 4d blues, we are referring to actually a "Reduction" reaction.  (Oxidation occurs when a reactant loses electrons during the reaction. Reduction occurs when a reactant gains electrons during the reaction.) 

In fact, here it is thought that the "Reduction" is probably caused by atmospheric sulfurization (Coal burning for heat production, common in England/Scotland,  releasing H2S and So2). You will note, though, that stamp collectors commonly refer to sulfuretting as "Oxidation". But actually, for the sulfuretting of the 4d blues, it is chemically a "Reduction".  (Perhaps I should mention that I have a Chemistry degree.)

In addition,  it appears that the COGH 4d blue triangles used a pigment ink called "Prussian Blue". (Similar blue stamps of the era have been proven to have that pigment.) 

It is actually an Iron based pigment (Fe++/Fe+++), not lead (Pb). 

With sulfuretting, the Fe+++ ion becomes Fe++ (receives an electron). With Oxidation (such as using Hydrogen Peroxide on the sulfuretted stamp), the Fe++ ion becomes Fe+++ (loses an electron).

More information....

Some collectors may be interested to know how SO2 & H2S can lead to changes in Fe++/Fe+++ within the Prussian Blue pigment found with the COGH 4d blues, and consequently lead to sulfuretting?  And how does H2O2 reverse the process?

More specifically, how can the Sulfur compounds Sulfur dioxide (SO2) & Hydrogen Sulfide (H2S) be reducing agents that can change Fe+++ to Fe++?

And how does Hydrogen Peroxide work as an oxidizing agent and change Fe++ to Fe+++?

For those that would like to see the actual chemistry notations, here it is.... 

Oxidizing agent that can be used in the changing of Iron (II) ions to Iron (III) ions.

Hydrogen Peroxide  H2O2 + 2 H(+) + 2 Fe(2+) Reacts to  2 Fe(3+) + 2 H2O


Reducing agents that can be used in the changing of Iron(III) ions to Iron(II) ions.

Sulfur dioxide     SO2 + 2 H20 + 2 Fe(3+) Reacts to  2 Fe(2+) + SO4(2-) + 4 H+

Hydrogen Sulfide   H2S + 2 Fe(3+)  Reacts to  2 FE(2+) + 2 H(+) + S

Part B

Although the explanation above is certainly feasible, there could be another explanation for sulfuretting. Here is a possible alternative. In this scenario, the Prussian Blue pigment is not directly involved.

Prussian Blue pigment is a very deep intense blue, and sometimes whitening (or diluting agents) were added. Was, for instance, "Lead White" added by Perkins Bacon to the Prussian Blue ink for the COGH triangles? (I have no knowledge if this is true or not. I did find that the ink analysis of the DLR 1862 Confederate States of America Scott 6 5c blue "Jefferson was a combination of Prussian Blue (blue) and Talc (white)).

If so, the Lead White (Basic Lead (II) Carbonate - 2 PbCo3-Pb(OH)2) is subject to a degradation process: its surface is blackened on contact with Sulphides in the air causing a chemical reaction of Lead Carbonate to black Lead Sulfate. Could this be the cause of sulfuretting? It is possible.

Comments appreciated!