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The thing I like most about a liquid filled case is the incredible visibility at extreme angles and underwater. The liquid has the same refractive index as sapphire, so the hands appear to float on the top surface of the crystal. Also, there is no possibility of moisture condensation on the inner crystal, and the tick noise of the quartz movement is almost entirely dampened. And since liquids are incompressible, my Sinn UX case is rated to 12000 meters.
There is just one problem -- the battery change on my UX must be done in Frankfurt every 7 years. Here is the notice on the US authorized dealer website.
So I took that as an engineering challenge. How hard could it be? What fluid do they use? They used to use a silicone oil, but it discolored over the course of a few years and created a lot of warranty issues. Then Sinn made the switch to an unnamed fluorinated liquid. Since the whole battery and movement are submerged, the liquid must be a dielectric (insulator). The only fluorinated dielectric fluids are made by 3M and Solvay, and are marketed as Fluorinert and Galden respectively. These are "perfluorinated" hydrocarbons, which means all the hydrogen is replaced by fluorine. This fluorine functionality makes a compound extremely inert. For example, Teflon is perfluorinated polyethylene plastic.Under no circumstances should anyone other than Sinn attempt to open the case on an oil filled watch. Only Sinn in Germany has the equipment to properly service the watch because of the oil filled case. Our US service center RGM (as well as other watch repair centers in North America) cannot provide service for this model or change the battery, and to attempt to do so will damage the watch.
There are several grades of 3M Fluorinert with differing viscosities and vapor pressures. I selected one grade with properties similar to water. The molecular structure is like octane (petrol/gasoline), but with all the hydrogen atoms replaced with fluorine atoms. It is odorless, crystal clear, and nontoxic for ingestion -- though not recommended to drink! It can hold back 35000 volts over a 0.1 inch gap, so you can immerse electronics directly. Price is on the order of $1000 per gallon which works out to a few dollars per watch case.
I purchased some Fluorinert and tested a spare Ronda 715 movement in the fluid and found that it runs great while fully submersed. The Ronda 715 in the C6 Kingfisher watch actually has more torque than the ETA 955.652 Thermoline in the Sinn.
https://www.christopherwardforum.com/vi ... php?t=4960
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