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seven factors for highly effective watch replating

factor 2 - hardness of the gold plated layer: Its not enough to have a thick goldplated layer if it is easily rubbed off from casual contact with clothing, skin and other surfaces. If the gold plating is soft it will be easily worn off over a short period of time. This will be especially noticeable around the high points of the watch and the primary edges near the lugs. Without overstating this point, one should keep in mind that surface hardness and toughness of the final gold plated layer is extremely important if you expect your watch to be resistant to scratches and incidental abrasion. Good surface hardness will help prevent your replated gold watch from looking pretty worn and tired in a very short time (4-8 months).

Unlike goldplating thickness, hardness for goldplating is no longer regulated or specified by the FTC (as of august 1999). The manufacturers within the watch industry have technical guidelines for recommended hardness that are still utilized on newly manufactured goldplated watches.

Commercial electroplating shops who goldplate objects such as plumbing fixtures will defer to Military Specifications for finish hardness specifically MIL-G-45204C. In that specification, hardness for goldplating is referred to as "grade" (see chart e). For our replating applications, we will rely on this aspect of this specification for determining the standards for the different levels of hardness available for gold plating of watches.

Based on Military Spec MIL-G-45204C, Grade refers to the standard for the hardness of the goldplated layer. In the electrical engineering world, different surface hardnesses are needed for specific performances relative to conductivity, solderability, and abrasion resistance. In contrast, for decorative plating applications, surface hardness of gold plated finishes are not regulated or defined by U.S. FTC regulations as of August 1999.
grade	knoop hardness *
grade a	90 minimum
grade b	91 - 129
grade c	130 - 200
grade d	201 and over
* Knoop hardness is calculated by measuring the indentation produced by an elongated four-sided pyramid shaped diamond point. Pressed into an electroplated surface under loads (usually less than 1 kilogram-force) the indenter creates a 4 sided impression. Knoop hardness (HK) is calculated using the formula HK=14.229(F/D2). F is the applied load, D2 is the area of the indentation measured in square millimeters. Hardness numbers are cited relative to specific load values that were used in the test.
chart e	different grades expressed in Knoop hardness for gold plating finishes

The standard for measuring the hardness of gold plating is expressed as "knoop hardness". Knoop hardness is calculated by measuring the indentation produced by an elongated four-sided pyramid shaped diamond point. Pressed into an electroplated surface under loads (usually less than 1 kilogram-force) the indenter creates a 4 sided impression. Hardness numbers are cited relative to specific load values that were used in the test.

Now for most of us this is probably more detail than we want to know. The important thing you should realize is there is a way to designate the level of goldplating hardness for your watch. From the author's viewpoint, the knoop hardness value for your replated gold watch should be rated at least 110-130 range (grade b).

This hardness value will provide good scratch resistance and long term finish durability for your watch. You could designate a harder finish, however the tendency toward embrittlement of the goldplating can become an issue. In some cases this could lead to minor chipping of the heavy goldplated layer, particularly on the sharp edges and prominent design contours of the watch.

If your electroplating shop has not heard of knoop hardness and does not know what you mean when you ask about hardness in general, you should take your watch and beat a hasty retreat. There is a good chance the electroplater is not the one you want replating your valued watch. The good news is that most competent and qualified electroplaters can provide you with the correct hardness for your goldplated watch.

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