Pink Back Plate Block... 409 Or Unlisted 425?

Working on the ID first ... 425 is a perforated stamp.
You have a 409, the single line USPS being faintly visible.

True... by (physical) definition : imperf, single line, and as
defined by plate number (same used for 425)... a 425 is 'born'
a 409, prior to perforating.

But, begs the question... are there any recorded pink backs for 409?

I'd like to hear from a few experts on this one... thanks.

They exist on 425, so it is likely that at least some 409's would also be pink backs.

Yes, both stamps were produced from the same sheet stock. I have 409 with Schermack type III and Mailometer type IV in my collection with pink backs.

Belasco made reference to 409 pink backs in his book, Guide To United States Vending and Affixing Machine Perforations 1907-1927.

Both the PF and APS have 409 pink backs in their certification archives. There are currently several 409 pink backs listed on ebay.

Gotta ask, how do these get "pink backs"? Is it the effect of aniline ink, or something else?

kcaramat ~ thanks. That stated, it begs the question as to why Scott only references analine under 425, solely, and not, also, under 409...

The Scott catalog has many omissions. Perhaps they think it goes without saying. I have a friend that worked with them adding things to the catalog. It's a very slow process. I had high hopes for some of the changes to be implemented.

I anxiously waited for the New catalog to be released. Many changes were made, some were partially made, others were not made. It was disappointing. I had hoped for better results.

When you consider the amount of information in the Scott catalog, maintaining and revising it is daunting task. I can't even imagine undertaking such a project on an annual basis.