I constantly record appearances of Bourne engravings when they appear on eBay, eBid, Amazon and elsewhere. About once a year I review the times I have seen Bourne's engravings in the marketplace, regardless of whether they sold or not. I then revise the following rarity system. The purpose of the rarity system is not to be exact, but to give collectors a feeling for how rare or how common each print might be.

Bourne engravings are constantly available for sale on eBay, eBid, Amazon and elsewhere. I do NOT sell engravings.

There are several possibilities why engravings are designated as "unknown" rarity.

• Questionable attribution to Herbert Bourne. Sellers occasionally attribute engravings to Bourne which stylistically seem to be the works of others. Dates might seem wrong or occurrences don't seem to agree with other known appearances. Mistakes have occurred and may have persisted for years until prints were examined in person.
• It is not uncommon for amateur sellers to mistakenly describe lithographs and photogravures as engravings. So far, no lithographs have been positively identified as Bourne's.
• It is not uncommon for titles to be mistakenly transcribed. This is especially true when sellers are unfamiliar with subjects of engravings.
• Some engravings are extremely rare. It is possible that some engravings have been referenced only from their appearances in books and they may not be known as individual prints. A few prints have been referenced in museum collections and no examples have been seen elsewhere.