Materials

Stainless steel

The most popular material for watch cases, bracelets, buckles and clasps is stainless steel and in particular a steel alloy called 316L.  316L is regular steel but with 16% chromium added (the 16 part of the number), 10 to 14% nickel, and with a reduced carbon content (the L bit) of not more than 0.03%.

 

The addition of chromium and nickel means that 316L steels present very good corrosion (rusting) resistance as well as being nice and shiny.  They’re not completely rust proof though, so you should wash down a stainless steel divers watch with fresh water after use.  There’s a clue in the name, ‘stain-less’, not ‘stain-free’, which most architects don’t appear to have noticed and has led to the tendency for buildings that use it as an outside material to take on a horrible stained appearance after a few years.  


The low carbon content in 316L reduces the alloys brittleness and increases its toughness.  With watch cases it's not just ultimate strength that's important but also the toughness.  Glass for example has an ultimate yield strength greater than most steels, but because of its low ductility and low toughness it's too brittle to make a very good watch case material.  In case you were wondering about ceramics, they're pretty similar to glass in material behaviour.

 

316L is often called surgical or marine grade steel as it is useful for these applications.  You can also refer to it as 'knife & fork' grade steel as most cutlery is 316L.  A few watch makes use 904L stainless steel, which has a lower chromium content and therefore is slightly duller in appearance.

 

Titanium

The nickel content of alloy 316L watch cases can cause an allergic reaction on some peoples skin.  If you have a nickel reaction then you need a hypo-allergic watch material, which essentially means you need to buy a Titanium or Gold watch.  If your wife/girlfriend comes up with this as a reason for needing a gold Cartier then full credit to her.

 

Titanium watches are typically made from standard aero-space grade titanium alloy, which consists of 90% titanium, 6% aluminium and 4% vanadium.  ‘Alloy’ just means a mix of different metals, so a stainless steel watch is also an alloy watch, and an alloy wheel on your car could be made from pig iron and tin and still be an ‘alloy’.

 

Titanium is more expensive than stainless steel, but given the small amount of material actually used the cost difference is insignificant.  Titanium is almost half the weight of steel and also pretty much impervious to corrosion.  

 

Gold

Gold watches come as either 9 or 18 carat, and occasionally 15 or 22 carat.  Pure gold is 24 carat, so 9 carat gold is 9/24 ths pure.  9 carat gold is therefore an alloy that's mainly composed of other metals such as silver, copper and nickel.  The other metals provide the strength and hardness, but since their is no specific percentages it's impossible to state whether a particular gold watch will be more or less susceptible to dents and scratches than steel or titanium.

 

Why is pure gold called 24 carat and not just 100% gold?  Well, the answer is the same as why there are 24 hours in a day; it’s all due to the Sumerians (the guys that first invented writing in 3500bc) and their use of a base 12 numbering system instead of the base 10 system we use today.  Also the reason for 60 minutes in an hour, 60 seconds in a minute and 360 degrees in a circle, as all are base 12 numbering.  There is a logic in it though.  If each finger represents 12 then it’s quite easy to show a full hour as being a hand held up with all fingers and thumb extended (5 x 12 = 60 minutes).  And a full days work of 12 hours can be by 4 fingers and no thumb; each finger now representing 3 hours.  A finger has 3 bits to it,  bend your finger and you’ll see what I mean.  So now you can count off hours on one hand and minutes on the other, which is impossible to do using the modern base 10 numbering system.  Incidentally none of this is related to the traditional British two finger salute.  The two finger salute comes from the Hundred Years' War with the French (note 1 at bottom of page) where they used to cut the two bow fingers off any British archers they captured.  The salute is to remind the French to be careful.  I have no idea what the American one finger salute is all about, but I'm sure it has equally significant and historic origins.

 

Gold watches are often sold as completely hypo-allergic and utterly impervious to corrosion.  Whilst this is just about true for 18 carat gold, it’s not the case with 9 carat, which can readily dull and might invoke a nickel reaction to sensitive skin.

 

A chunky 18 carat watch can be quite weighty since gold is 3 times as heavy as steel.  This is not necessarily a bad thing though since a watch is normally worn on the left hand and most men, for no reason ever identified, have stronger right wrists than left ones.  A chap with a big gold Rolex is simply someone who must have well developed right wrist muscles, perhaps a writer or something similar, and wants to balance it out a bit. 

 

 Note 1: The Hundred Years War lasted for 116 years.

Quality, Strength, Performance