That 904L was used in Rolex watches was really never in doubt, the question was more was it the case and back? Your post doesn�t specifically confirm that, but I assume you intend it to mean it does. Is the case back 904 as well as the case? Now, that�s an interesting question�..
�Allergies due to higher nickel content? No, because they are using an ALLOY,� I don�t know your background, but unfortunately I�m afraid that betrays you�re getting a bit out of your depth on this topic. Everything metallic can be called an alloy apart from pure metals. There is pretty much no argument over the high nickel content of 904L, the question is one of �What�s the data for the nickel release?�
Nickel release: Should be no more than as follows - on one square centimetre of skin no more than 0.5 micrograms of nickel may be released within one week. This limit may not be exceeded by any product that is in direct contact with the skin for a long period of time. In some countries this is law. The strength of nickel release is not ascertained by the nickel content of a metal, but rather by its resistance to corrosion. Only during corrosion processes is nickel in the form of ions or complexes able to leave a steel structure. In very corrosion-resistant steels, nickel remains stably bound to the steel despite its possibly very high nickel content. 316L cases can operate at about 0.01 micrograms per cm2 per week (1/50 of the limit). I have no data for nickel release of 904L (anyone?) So we still haven�t answered that question. There is also the fact that people who seem sensitive to nickel pick up their rashes at release levels far below the recommended level. The way the surface is work hardened and even the texture has a significant effect on Nickel release and can make differences of 10 to 100 times locally.* So, it is just not possible to generalise the way you have that 904L will be ok or is better than 316L. These effects also go someway to explaining why it is very hard to get a solid view on the pattern of people�s nickel allergy in relation to the watch cases they wear.
Corrosion resistance: Under extreme conditions not related to watch wearing, 904L does have specifically superior corrosion characteristics to 316L, but having used 316L at up to 850 deg C in oxidising and corrosive environments professionally, I seriously doubt any watch wearer will gain any benefit from 904L other than a feel good factor, and the aesthetics of the colour and sheen. Well, unless they live for days on end at the bottom of the sea next to a lava source as the sea water needs to be warm (and I mean 60 deg C and up).
Hardness. Generalising about how the 904L cased Rolex shrugs off scratches compared to Omega based on magazine reports is also pretty worthless. Raw 904L is actually factually softer than raw 316L. The question is more �what hardness is delivered in the final products?� More a question of process than base alloy. Rolex may well have a process that delivers slightly harder cases than average whether they use 904 or 316L. Has anyone hardness tested the cases of all the leading watches in the lab? If someone can send me a suite of cases of interest, I�ll get them hardness tested, but they will have an indent on return, so only scrap ones please��..
Finally, why get so steamed up about the use of 904L? There are actually far �better� steels depending on your needs � so Rolex is not using some kind of �ultimate� anyway � it�s just their choice. Maybe Rolex should consider 2205, greater mechanical strength, similar corrosion resistance and it�s cheaper�..
I lived with a materials scientist specialised in metallurgy for more than a decade and if she saw your post she�d punch you on the nose! The use of 904L is a very emotive issue and we have to be razor sharp about the facts. Please take this in the nicest possible way, and in the spirit of �if you wouldn�t say it at a dinner party, don�t say it on ThePurists.� I come to the ThePurists because of the clear superiority of the exchanges compared to other fora, with the intention for everyone to prosper from increased knowledge. You post has flushed me out to hopefully write something useful and beneficial, but I wish the tone you wrote your original post in was more along the lines of �here is some info I�ve found,� rather than the whole �Rolex is best� tub thumping yet again, based on anecdotes and alleged authorities (which I�m getting pretty tired of).
* SOCI�T� SUISSE DE CHRONOM�TRIE NEUCH�TEL Relargage du nickel et corrosion par piq�res des aciers inoxydables. Influence de la direction de laminage P.-Y. Eschler, L. Reclaru, A. Blatter PX TECH S.A., Groupe PX, CH-2304 La Chaux-de-Fonds
the reference I posted above (Eschler et al) concluded that work hardening the surface INCREASED the rate of nickel release. Thus there is a difficult balancing act to perform here for manufacturers. Of course you can have a lower hardness on the back, higher on the front�..
Finally, 904L doesn�t appear to be a magic cure either as Patekkie has already got a reaction from his Daytona. I think all this proves is how far there is to go in understanding nickel release!
I wasn't going to write anything more on 904, but I can't let that stand.... I'm sorry but you CANNOT draw those conclusions.
In the end the 904 thread still really threw up more questions than answers and still did not really have concrete output on 904 v. 316. Even the data sets from industry studies are moderately contradictory (probably partly because of their meagre sample sizes.) My own experience, years ago, developing a surface treatment process for adhesive bonding of the then new Al-Li alloys (with durability tests for c. 1000 hours in seawater spray at 60 deg C) threw up MASSIVE variability issues and you needed huge numbers of test samples to extract statistically meaningful results. This was done because people's lives were in danger in the aircraft made from them. I'm afraid that nobody is going to get to the bottom of this Ni release issue in the foreseeable future because the study needed would be hugely expensive and nobody is going to die from a Nickel rash (touchwood) so nobody will bother!
I keep seeing hopeful conclusions drawn (I've looked on other watch websites) on the basis of people having looked up some broad properties of these materials and read "904 better than 316 in salt water. Ergo, Rolex better than everyone else�. I have already moaned about this "a little knowledge" issue being very dangerous. (Sidebar: What nobody ever bothers to report when they read these charts, is that whilst 904 is great for sulphuric acid transport, it's poor for nitric acid and in fact 316 is better and in fact 304 (a much 'lowlier' stainless grade) is probably one of the best for nitric. Etc, etc, yawn yawn....)
Bottom line? There are so many variations even in the lab tests from the alloys alone, let alone their surface properties (hardness, texture etc) from the data I've seen when added to the real world of people's body chemistry and so on, we can draw next to no meaningful conclusions at all. Well, other than,
1. Boy, this Ni release issue is way more complex than we realised.
2. The alloy composition is only as (or arguably LESS) important as several other factors - surface texture, hardness and skin secretion properties!
Once again in the nicest possible way - I am also concerned that you are participating in threads with little to no interest in other views or more importantly FACTS. Patekkie posts he got a rash off a watch with a case of 904 and you post �Thus, magazine writers and others need to quit talking about the possibility of rashes with Rolex.� Duh? Are you actually reading this stuff?
Based on your track record of posts, you can't really be given the benefit of the doubt so I'm afraid that it is either your Rolex heart overriding logic, the desire to have the last word, or try to prove that you WERE right after all that leads you to draw these repeated erroneous conclusions.
As you correctly stated, the allergic reactions are the result of the Nickel release, which is independent from the alloy's Nickel content. 904L contains about 24% Nickel, 316L 11%. The degree of Nickel release is directly connected with the material's resistance against corrosion. As a result, 904L releases in fact less Nickel than 316L. The latter's Nickel release rate is barely under the EU regulation 94/27/EC, which demands a release of not more than 0.5 mu-grams/per square centimetre per week. 904L is below that, at about 0.3x.
The material supplied to me compares (among other alloys) 14539 (B�hler A962 - 904L) with 14404 (B�hler A200 - 316L). There are two tests: the classic DMG test, which is a very quick and simple test: the test piece is wiped with a pad, containing a specific Ni reagent (Dimethylglyoxime). Nickel release is then indicated by a pink red colour. The other test is more interesting for materials that are in direct skin contact: the test material is exposed to 3x concentrated synthetic sweat for eight days, at a temperature of 40 deg. Celsius.
I just got a paper showing various test results from the Austrian steel manufacturer Boehler, who is the supplier of the steel used for the Rolex cases and bracelets.The paper is s lecture, held by B�hler technicians during the Euromat congress in 1999. I have a PDF-file, if you want, I can mail it to you.
Thanks for at least finding a data point for 904L! But, based on 316L experience, there's probably a very broad range of values of Ni release for 904L as well - depending on finish, work hardening, local stresses left in the surface, etc, the release rate has been shown to vary by 2 orders of magnitude in 316L.
If the data for the 904L is from a finished case on test then bravo Rolex, they're 70% inside the EU guideline. However, Sinn published a NI release rate 98% inside the EU limit for their standard 316L cases - their Tegiment case is even lower.
My point is only that there are massive variations here likely swamping the effect of the alloy and more to do with manufacturing process and finishing.