Elinvar vs. Nivarox vs. Parachrom

[chris russell]

A few people have posted inquiries about the new Parachrom Blu hairspring Rolex is installing in new watch designs as they appear, (first in the Daytona, then in the Milgauss, then the DSSD, the GMTIIc, and the new Ceramic Subs). I spent a little time looking into the characteristics of Parachrom in comparison with two other popular alloys used over the years. These alloys were designed to solve two problems with the earlier blued steel hairsprings: thermal instability and magnetic susceptibility, (plus a third problem with steel; rusting).

Steel has a relatively large thermal coefficient of modulus of elasticity. That is, its 'springiness' varies with temperature, necessitating complicated and only partially effective compensation schemes in the balance assembly.

Steel is also strongly affected by magnetic fields, leading to distortion and magnetization which drastically affect timing.

Among the first alloys to minimize these issues was Elinvar, a mixture of 59% iron, 36% nickel and 5% chromium, invented in 1919 by Charles Guillaume. The chromium reduced but did not eliminate the other two (ferrous) metal's susceptibility to magnetization, and the alloy's elasticity varies very little with temperature. This made possible accurate watches without complex schemes for thermal compensation, and providing watches with 'anti-magnetic' properties for the first time.

An improved alloy, Nivarox, came along in around 1933, invented by Dr. H. C. Reinhard Straumann, consisting of about 45% cobalt, 20% nickel, 20% chromium, 5% iron and smaller percentages of titanium and beryllium. The exact proportions of the metals in the alloy varies with the specific application. Although cobalt, nickel and iron are all ferromagnetic metals, the high proportion of chromium further damps the alloy's response to magnetism, better than Elinvar, though there is data showing Nivarox's thermal coefficient of modulus of elasticity is not quite as good as Elinvar's, and possibly not quite so predictable in production.

Both alloys have good resistance to magnetic fields, though not complete, due to their heavy proportion of ferrous metals. In 2000, Rolex, after several years of experimentation, introduced another alloy, 'Parachrom', this time made of entirely non-ferrous metals, (85% niobium and 15% zirconium), which was carefully mixed in proportion to deliver a nearly zero thermal coefficient of modulus of elasticity. Although both of these metals are strongly resistant to corrosion, Rolex found that by deliberately coating the alloy with a thin, (roughly 100 Nm), layer of oxide, coincidentally a beautiful blue color, its stability with time was even further enhanced. Thus in 2005, the Parachrom hairsprings turned blue, and Parachrom Blu was introduced.

This new alloy appears to all intents to be the finally almost 'perfect' hairspring material; completely insensitive to magnetic fields, showing almost no response to varying temperatures and virtually impervious to long-term corrosion or change in characteristics. In addition, Rolex claims that it is far more stable with mechanical shock than the older alloys.

I have and have had a few Rolexes with this Parachrom hairspring, and I can report that they are almost spookily stable with position, (perhaps due as much to the Breguet overcoil), with daily use showing almost no 'drift' in timing over many months. I subjected one of my Daytonas to freezing temperatures with no discernable change in timing. Admittedly, my Rolex with the older Nivarox hairspring is almost as good in these respects, but the Parachrom seems just that much better.

To me, this goes a long way toward proving Rolex is committed to staying at the leading edge of mechanical watch accuracy and reliability.

Incidentally, as most of you know by now, the latest issue of 'Watchtime' (with the green-dial Rolex Sub on the cover), contains a fascinating article which among other things delves into the very careful alloying process Rolex performs in its own factory, to produce the metal for these hairsprings.

I welcome comments or possible corrections if any factual errors crept into my post. Thanks.