One way of evaluating the age of a brooch is by looking at the fastening (although you must of course take everything into consideration). There are some hard and fast rules that can be applied but there are also exceptions. You must take into account that a brooch might have been remounted with a more contemporary mount (or, in rarer cases, remounted on an older mount). Also, it's important to look at both the pin, the clasp and the hinge.
(For clarity's sake, a brooch consists of: the pin i.e., the sharp metal piece that pierces the clothing, the hinge, i.e. the part that allows the pin to pivot, the catch, i.e. the part that holds the pin in place. The main, decorative part is called the body and all else are called findings.)
Presuming it has not been remounted or modified, the follow rules of thumb apply for dating brooches:
The basic c-clasp brooch (or 'pin') fastening was used through out the 19th century and into the 20th century (ending around 1910).
C-Clasps were nearly always hand-made.
C-Clasp extending beyond edge of brooch
Remember: as the 19th century progressed, the pin generally got shorter and finer.
'T-Bar' or 'Tube' Hinges
From around 1850 to 1910 (Also used in other eras to a lesser extent)
These hinges were made by hand and consisted of three cylinders or tubes, one attached to the pin itself, the other two to the sides of the pin.
The 'T-Bar' hinge narrowed and became finer in the early part of the 20th century.
It is important to note that although the hinge of the C-Clasp narrowed with time, the actual clasp itself could be broader in more recent times.
Ball-Style or Round Hinge
In the early 20th century, around 1920, the 'T-bar' or 'tube' style hinge was replaced with a rounded, 'ball-style' hinge.
These hinges were machine-made and became standard around 1930.
The pin itself became one single piece, as opposed to a pin soldered to a tube or cylinder, as with the 'T-Bar' or 'Tube' Hinge.
Early Safety Catch (has a movable piece)
All of the below were invented post-1849
They were hand-made until the late 1920's
Early Safety Catches were created to prevent loss of the brooch from the clothing.
These were usually one of the following styles (although there were lots of creative variations):
On a lever catch, you find a small piece at the top of the clasp to lever the catch open.
Often used on small brooches
SAFETY PIN CLASP WITH CHAIN
Safety pin clasp.
A safety pin was embedded into or attached onto the body.
Trombone Catch (or 'push-pull catch')
This is when a pin slips into a barrel. Specifically European pieces.
Tube or Barrel Catch
These were similar to the trombone style catch but without the push-pull mechanism.
Locking C-Clasp (early Roll-Over Saftey Catch)
Patented in 1901 / Widely used from 1910 onwards / Handmade until late 1920s
These used a spinning locking mechanism.
Early locking C clasps opened downwards, and more modern ones open upwards.
Early locking clasps usually had a small rounded mechanism.
Later versions ones had a locking piece that was separate and slipped over the holding piece of the clasp.
Modern Safety Catch
Machine made roll-over, locking or safety catch as we know today.
Became widespread in the late 1920s to early 1930s.
Usually combined with a round hinge and often pre-assembled as a single unit, bought separately and added to the piece by the jeweller.
Dress CLips or Double Clip Brooch
1927 (spring system patented by Cartier)
1931 (mechanism patented by Coro)
These gained popularity in the 1920s and were worn until the 1950s. Quintessentially 'Art Deco'.
Double clip brooches could be worn separately as dress clips or together as a larger brooch. They were sometimes placed on bags and scarfs and fur coats as well as on clothing.
Double Hinged Clip
(or 'Fur Clip)
1928 (patented by Cartier)
Designed to hold on to thick pieces of fabric, these involved a double pronged clip with a heavy-duty spring mechanism. Although these were known as 'fur clips' they generally weren't worn on fur as they would have ruined the pelt.
Note: When testing for karat, do not test the fastener or rely on the karat markings of the fastener alone.
Sources / further reading:
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