Wednesday, 24 August 2016

Gold Plated Watch Cases

The gold plating of watch cases can be rather confusing, this post is an attempt to demystify what should be something quite straightforward, unfortunately there are, as ever, some wrinkles often caused by unscrupulous makers and resellers, normally at the lower end of the market and by the lack of legislation on the subject nationally and internationally at the time pocket watches and their cases were being made..

I will be looking at the manufacture of the fabric of the case, not the gilding of silver and other processes used for applying ornamentation of a case (or movement). So only two processes need to be considered, electro plating and pressure welding of solid gold to a brass or composite substrate or core.

Electro plating using a number of different processes was only used on the outside on very cheap cases as being very thin it goes not wear well, but is was used on the inside of cases in combination with pressure welded plating on the outside.

Pressure Welding.

One way of permanently bonding two metals is to put two or more plates together and then to put them through a rolling mill which as well as reducing the thickness and the great pressures involved will cause the surfaces to become welded together.

Filled & Rolled Gold.

Although, at the time, there was no legal definition of these terms - in UK a proposal was made but the legislation never materialised - it was generally accepted that Filled Gold was made by pressure welding a plate of solid gold to each side of a core which was normally a composite / alloy of brass.

Rolled Gold was a single plate of gold pressure welded to one side of  a core with the other side electro plated.

Case bows and links of watch chains were made by a similar process with gold wrapped around a central core and then pressure welded, this was classified as rolled gold, even if the watch case as a whole was "filled" gold.

The thickness of the gold plate was a determining factor in cost and durability. Higher quality gold, normally 14 carat, being softer would need to be thicker to give the same durability as a 9 or 10 carat plate.

Dennison Cases

The Dennison Watch Case Company, based in Birmingham, was second to none worldwide in the volume production of watch cases and fortunately some of the technical specifications of their cases are known:
  • The Rolled Gold "Star" grade had a 9 carat gold plate thickness of  0.036mm and were "warranted" to last 10 years.
  • The Filled Gold "Moon" grade in 10 carat gold had a plate thickness of 0.072mm and were warranted to last 20 years.
  • The Filled Gold "Sun" grade in 14 carat gold also had a plate thickness of 0.072mm so it is little odd that these cases had a 25 year warranty being softer than the 10 carat Moon and of the same thickness. But of course all three grades normally outlasted the warranty and if a Sun grade lasted only 20 years I doubt the owner would have been perusing the issue after all that time.

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