US # 39-S "Specimen Stamp

I have a US #39 with magenta crossed lines on it. The APS expertized it as a #39-S specimen. There is no listing in Scott Specialized for this stamp as a specimen. I found an image from an auction that matched and looked it up in Seigel power search. Turns out these are called a control mark, "found on various 1857 issues and were probably applied as a Specimen mark" as stated in the Seigel listing. The odd part is all three of their #39 specimens were unused, as they all are. But this one was expertized by APS as both a specimen and used. It has a black cancellation in the corner. Assuming the APS expert is correct, has anybody here got any experience with early US postally used specimen stamps?

Could you show us both sides? I doubt if any one has much experience with used Specimen stamps.

I would not call a specimen "unused" or "used", but as a separate category.
It is obliterated in a way to prevent it from being used, but it was never actually used.
I would label it a "specimen", and stop at that.
But, I agree with littleriverphil, illustrations are a must.

Sorry for not uploading the images with my first post. Here they are. There is part of a circular black cancel in the upper left corner. The APS expert apparently felt the cancellation and the magenta lines are both genuine although I have never heard of a specimen stamp used for postage. This is kind of an oddity in that it has the crossed lines rather that the SPECIMEN overprint.

Since the magenta cross was intended to demonetize the stamp it is highly unlikely that it traveled though the postal system. The cross essentially canceled the stamp and removed its service value.

Does not look like a part of a circular cancel to me.

The stamp is not on a cover or piece, so its alleged "used" context is completely absent - whether even an actual cancel, whether used somehow, whether favor-canceled maybe even decades later or ? The 90 cent value doesn't have many common uses either. Speculation at best.

Yes I agree the black mark is faint and doesn't look much like a postal cancel. I originally thought the crossed lines were a cancellation and that is why I sent it in to APEX. So when the certificate came back as "used, specimen lines" I started looking into what that might mean. I know APS uses a spectrophotometer to find ink cancellations and determine their identity and composition (new, old, post office, home made, etc.) so if they call it used in addition to the specimen lines I am left wondering. I tried to upload the certificate but the file size is too big. It is APEX certificate 234829 if anybody is curious. I think my next step is to send it to PF or PSE for another opinion. Any recommendations are welcome.

Do you have any direct knowledge what analytic tools they used with your stamp? Having tools, doesn't mean using them on every submission. I fully doubt the APS did any composition analysis of the black "cancel" area.

There is nothing proprietary about the ink formulation the Post Office Department used in any given era, and much ink was obtained locally - thus some natural variation in chemistry and quality. There are additionally, some greater chemical differences between inks from many decades apart. I see this as well beyond any APS analysis needed for this stamp.

Add: What do you expect another certifying service to tell you?

To be candid you are going to end up spending more than the stamp is worth on expertizing fees.

Well it turns out this is not a used SPECIMEN stamp. APEX is issuing a replacement certificate recategorizing it as unused and removing the word "used" from the description. This new certificate will align with all of the other SPECIMEN stamp certificates they have issued.
I hope you can understand and forgive my confusion and wild thoughts of having something unique. Case closed.