What theoretical advantage, if any, does a duo-in-uno hairspring possess over a helical hairspring?

[Incroyable]

I have an interesting duo-in-uno watch.
Unfortunately an orphan, and in terrible condition.
Fascinating though.
Negus Brothers #5688. From around 1884, I believe.

All of the steel components have an interesting black finish that I've not seen before.
The screws, springs, all the motion work, the balance wheel and the spring, even the pinions and arbors have this peculiar black finish.
Looks like it was all powder coated or something.

The hairspring is very distorted, sadly. What has always caught my attention, besides the duo-in-uno, was that the spring is very thick. Almost square stock.

Regards,
Steven

View attachment 738472 View attachment 738473 View attachment 738474 View attachment 738475

Would this have been made for this specific Negus Brothers?

Thomas S. Negus (manufacturer) - Wikipedia

en.wikipedia.org

 

[Dr. Jon]

Yes it was this firm. They imported this example which was made by A. P Walsh. I have seen other examples, in much better shape.

 

[Incroyable]

Yes it was this firm. They imported this example which was made by A. P Walsh. I have seen other examples, in much better shape.

Were the other examples you've seen cased or uncased?

 

[Dr. Jon]

Most of the duo-in-uno sprung watches I have seen are also by Walsh but sold by Sam Hammond also of New York.

 

[Incroyable]

There was apparently an OF Parkinson & Frodsham duo-in-uno in its original gold case that sold last week at a local English auction.

A watchmaker acquaintance sent me some photos of it after the fact.

 

[Dr. Jon]

Also likely made by A. P. Walsh. The firm submitted two Walsh watches to the 1876 Geneva open regulating competition which listed as regulated by Walsh.

 

[Incroyable]

Here is the watch in question:

Parkinson & Frodsham. An 18 ct. gold free sprung open face pocket watch with up and down dial, Case and Movement No. 5710, London hallmark for 1873 enamel dial with black Roman numerals and outer five minute chapter, subsidiary dials for power reserve and subsidiary seconds indication, free sprung keyless wind movement numbered 5710, 18ct gold hinged case numbered 5710, hallmarked for 1873, and stamped HW possibly for Henry Webb, with plain gold dust cover, together with a leather and 9ct gol

 

[Incroyable]

It seems the Parkinson & Frodsham records are held by the London Metropolitan Archives. Has anyone looked through them before?

Unfortunately they don't seem to be digitized.

PARKINSON AND FRODSHAM | London Metropolitan Archives

search.lma.gov.uk

 

[Incroyable]

Another P&F duo in uno.

Facebook

www.facebook.com

 

[Bernhard J.]

What is thought about triple overcoil hairsprings? Is that sort of a duo-in-uno with a shorter helical part?

Cheers, Bernhard