Thursday, 15 October 2015

A Rare Rotherham and a bit about hairspings & balances.

A Size 12 Rotherham for Hoefler &
Co of Devenport. 19 Jewels, 1901.
This is at first sight a normal high end size 12 Rotherham with 19 jewels but two things make it unusual, first is still has an original watch paper in the back as described in my last post, but more important is the very rare balance assembly.

Normally these movements have a cut compensating balance with a normal steel Breguet hairspring, however in the late 1890's a new alloy known as "Elenvar" was devised by Charles Édouard Guillaume (who got the 1920 Nobel prize for physics for the development), its key property was that unlike steel its flexibility (modulus of elasticity) did not change with temperature. When used as a hairspring it removed the need for a compensating balance.

A very rare solid balance with an
Elenvar Breguet hairspring.
Most companies implemented the Elenvar hairspring with a screwed balance which allowed the balance to be balanced fairly quickly (as a car wheel with a new tyre) and the weight and number of screws could be used to adjust the moment of inertia to match the hairspring to make the watch run too time. 
With this movement Rotherham tried a different route and used a traditional 3 armed solid balance which is probably gold. Balancing and tuning was done by removing slight amounts of material from the balance as can be seen from the picture to the right..

This is the only watch I have seen with this arrangement and it is likely that Rotherham only made a few, probably because the amount of skilled work required to set up the balance would more than likely have made it more expensive than the normally sprung cut compensating balance.

Wednesday, 14 October 2015

A rare pair of papers.

click the picture for a larger view
It is very rare these days to find watches with watch papers intact (they are collectable in their own right), I had only 2 or 3 from the last 600 watches. And today two turned up together, I knew one was coming but the second was a nice surprise.
The papers were used for advertising and would have been put in by sellers or repairers and occasionally you find a watch with a stack of them but usually they are glued together, to the case and / or are falling to pieces. Both of these are original to the watch and have the same retailers names as are shown on the watch faces.
The blue one is on a Rotherham from 1901 retailed by Hoefler of Devonport. The watch itself is something rather special - watch this space!

The red paper is on a Waltham 1908-610 half hunter sold by Harral of Barnsley, it has the serial number of the movement on it and is dated 11 years after the watch was made so presumably they were warranting a repair or they had bought back the watch and had resold it.

Thursday, 1 October 2015

Dating Movements by Cyma & Tavannes

I recently had a query on dating these movements so have posted the answer here so I'll not have to do it again.

The serial number on these movements are under the dial as show to the right. My dating is based on a reasonable number of watches, listed below, in hallmarked silver or gold movements. The sample is heavily biased to watches retailed by J.W. Benson, largely because other retailers frequently used Swiss hallmarked silver cases which do not carry a date mark. Benson appear to have switched from Revue to Tavannes in about 1932 the database is only good for the 1930s.

It must be remembered that a movement might not go straight into a case which itself may have been on the shelf for a while so there will be some overlap, also the hallmarking years of the various assay houses are not in line with each other or the with calendar but the difference is small and the date is likely to be accurate to plus or minus a year.  (updated Feb 2017)

Serial Date
      4,322,549 1908
    12,487,883 1919
    14,708,666 1919
    13,079,475 1921
    14,262,246 1924
    15,485,579 1926?
    15,485,952 1926?
    15,939,146 1926
    17,482,498 1929?
    16,624,975 1930?
    17,865,828 1932
    17,886,973 1932
    17,888,724 1932
    17,888,811 1931
    17,889,975 1932
    17,899,152 1931
    17,899,219 1932
    17,889,918 1932
    17,902,501 1932
    17,903,525 1932
    17,903,625 1932
    17,908,930 1932
    17,909,034 1932
    17,909,035 1932
    17,944,833 1933
    17,944,871 1933
    17,966,044 1933
    17,970,131 1933
    18,045,354 1935
    18,045,567 1935
    18,050,727 1935
    18,052,802 1936
    18,055,283 1936
    18,055,497 1936
    18,055,498 1936
    18,055,544 1936
    18,066,750 1935
    18,070,392 1936
    18,076,649 1936
    18,090,883 1936
    18,112,605 1937
    18,112,379 1936
    18,113,219 1937
    18,141,556 1937
    18,146,434 1937
    18,146,664 1938
    18,199,372 1937
    18,240,750 1938
    18,245,978 1938
    18,246,001 1938
    18,252,273 1940 Benson stock?
    18,253,220 1939
    18,256,774 1938
    18,265,158 1938
    18,268,000 1940
    18,276,566 1947?