Silver Alexander Ritchie Annular Celtic Brooch Raised Knots and Serpents 1920s?

I love this antique, solid silver brooch which has an interesting history and most likely dates from the early 1920s.

A big, quite heavy, brooch, 5cm across and weighing 27.83g, it is hallmarked with AR (Alexander Ritchie) and IONA marks on the reverse side.

It is known as an annular brooch (forming the shape of a ring), with raised knotwork bosses and entwined serpents/beasts. I understand that the wonderfully crisp design could also be described as a zoomorphic decoration between spiral bosses, also known as sailor’s monkey knots or Celtic knots.

Serpents in Celtic jewellery are a symbol for rebirth, healing and wisdom, due to the cyclical shedding of their skin. The serpent was considered an immortal creature that came to life each year with a new skin. The Celts believed serpents slithered up from the inside of the earth and they held all of the world's secrets and divine wisdom.

I am guessing that the pin and clasp are a later addition, but I personally think this makes the brooch easier to wear.

With regard to there being no silver hallmarks for the assay office or date made (just A.R. and IONA), it does say on the Alexander Ritchie web site that:-

“During the early part of the 20th century, many items of silverwork were not hallmarked, and just carried the stamps AR and IONA impressed into separate rectangles”.

. . . which describes the marks on this brooch, so it may signify that it dates from the early 1900s, in which case, it is a rare example of Alexander Ritchie's work.

Interestingly, prior to 1910, the year Alexander Ritchie registered his own mark with the Chester assay office, pieces were marked CS*FS, as the firm of Cornelius Saunders and Francis Shepherd submitted Alexander Ritchie’s silver work to the Chester assay office.