In my recent research into the Defy Classic Skeleton, I found the Zenith product pages lacking in some technical details that I, as a deeply nerdy WIS, wanted to know. So I reached out to Zenith directly and was able to get some answers, as below.
Q1. What grade of titanium is the Zenith Defy Classic made of?
This is important because there's a vast difference between "commercially pure" titanium like the often-used Grade 2, and alloyed titanium. In particular the alloyed Grade 5 is ideal for watchmaking, being stronger, lighter, harder and more corrosion resistant than the defacto-standard 316L steel. You see a lot of debate on Steel Vs Titanium in watchmaking, and a lot of it is misinformed due to the often non-disclosed nature of which types of steel or titanium are being used.
If you'll allow me to geek out about this for a moment, lets get into the nitty-gritty of it:
Stainless steel (316L) offers a tensile strength of 485 MPa, a hardness of 95 on the Rockwell B scale, and generally excellent corrosion resistance. However, this alloy is subject to pitting and crevice corrosion in warm chloride environments. In many marine environments 316 does exhibit surface corrosion, usually visible as brown staining. This is particularly associated with crevices and rough surface finish.
Grade 2 (commercially pure) Titanium is generally less desirable than 316L for watchmaking, offering a tensile strength of 344 MPa and a hardness of 80 on the Rockwell B scale. However the oxide film formed on titanium is more protective than that on stainless steel, and it often performs well in media that cause pitting and crevice corrosion in the latter (e.g., seawater, wet chlorine, organic chlorides).
Grade 5 (Ti-6Al-4V, or an alloy of 90% titanium, 6% aluminium and 4% vanadium) is the best of the lot for watchmaking, with a tensile strength of 1170MPa and a hardness of 112 on the Rockwell B scale (converted from Vickers 396), while offering identical corrosion resistance to pure titanium.
A1. The Defy Classic Skeleton is made of Grade 5 Titanium
Great news on this front, and an excellent choice for a modern sports watch. Grade 5 should be more scratch-resistant than 316L steel, whilst also being lighter, "warmer" in feel (due to lower thermal conductivity) and immune to long-term crevice corrosion from swimming in chlorine or salt water.
Q2. Are half-links available for the bracelet, as the butterfly clasp seems to lack a micro-adjust feature?
A2. Links are very small and is equivalent to around about a half link in other brands.
So no real half-links or micro-adjust, which may be problematic for those who need to achieve a perfect fit, however the comment about the links being smaller than normal anyway is somewhat reassuring.
Q3. Your website notes that the escape wheel and lever are made of silicon, but does not specify the material used for the hairspring. Can I inquire what this is made of?
A3. Hairspring is Nivarox, with their own proprietary alloy.
Nivarox hairsprings are alloys of 45% cobalt, 20% nickel, 20% chromium, 5% iron and smaller percentages of titanium and beryllium. The alloy is not immune to magnetism (being made largely of ferromagnetic metals), but the high percentage of chromium does dampen its response to magnetism.
Q4. Following on from the previous question, does Zenith provide a Gauss rating for how magnetically-resistant this timepiece is, given the use of silicon in the escapement?
A5. As you are no doubt aware the whole movement needs to be protected in order to be anti-magnetic, either by a faraday cage or similar.
Something of an evasion of my question, but I understand the brand's reluctance to warrant any skeletonised timepiece as anti-magnetic. Given a Nivarox hairspring with a silicon escapement, I wouldn't be surprised if the Elite 670 SK is more resistant to magnetism than the 4,800 A/m that ISO 764 requires.
Q5. Do Zenith provide any guarantees of the daily timekeeping accuracy for this watch?
A5. There is no guarantees on accuracy as this is dependent on the wearer’s habits, surroundings, environment, care, etc. However, the watches all leave the Manufacture at an accuracy well within the COSC tolerance.
Interesting that Zenith watches are being tested to within-COSC specifications for timekeeping before leaving the factory. Some digging into the user manual for this watch also revealed the following:
Under normal conditions of use, the precision discrepancy
for our automatic watches is a maximum of 4 to 5 minutes
per month in comparison to the standards on the market.
So a maximum deviation of 10 seconds per day. While this sounds poor in comparison to say Rolex or Omega's warranties, it's pretty standard for a non-COSC certified modern timepiece. The Grand Seiko 9S movement is also warranted to +10 spd during regular use, for instance.
Q6. How long is the warranty period on this watch?
A6. Warranty is 2+1- additional 1 year warranty when you register your watch.
Again not great compared to Rolex and Omega (5yrs) or JLC (8 years), but better than the standard 2 years for most brands at least.
Q7. Are adjustments and regulations of timekeeping covered under warranty?
So at least if you start getting deviations greater than 10 spd Zenith will regulate your watch for free while under warranty.
Hope that's of some use to anyone considering a Defy Classic Skeleton, like I am. I just now need to decide whether I can accept accuracy in the 10spd range (even though I'm sure that anecdotally most Elite 670 SK's will perform better), and whether I can deal with no warranted magnetic resistance. I ended up trading away a Nomos Neomatik because I kept getting it magnetized, but that's a very slender watch with no silicon components in the escapement at all. I wonder just how much better the Zenith would fare in this regard.
Oh and if anyone's interested in substantiating any of the above, here are my sources:
ASM Material Data Sheet
ASM Material Data Sheet