# Yellow Crystals !!



## Melville (Jun 17, 2013)

Some older formulations of plastic crystals (pre 1950) yellow and release gas very slowly - nitrogen dioxide and nitric acid. This gas is trapped between the dial and the crystal, and can corrode the hands of the watch. Many older pocket watches had these fitted as replacements. Such as this Hampden circa 1917. The damage caused to the hands is so severe that they are falling to pieces. The rust is so bad that it rusted the 4th wheel pinion that carries the second hand so badly that a replacement 4th wheel will have to be sourced. So if you have any watches with yellow plastic crystals, change them for the new type that will not develop this problem.


----------



## Guest (Aug 2, 2015)

blimey :scared: , i have shooting glasses that colour...................MY EYES !!! :blind:


----------



## vinn (Jun 14, 2015)

could not that corrosion be from moisture rather than the crystal?


----------



## Guest (Aug 4, 2015)

vinn said:


> could not that corrosion be from moisture rather than the crystal?


to be fair, i have an old military pocket watch with a yellowing crystal and the hands are all but destroyed, but the movement is spotless


----------



## Melville (Jun 17, 2013)

The destruction of the watch hands on the Hampden is definitely caused by the chemical reactions of the polymers in these early plastic crystals that turned the plastic yellow or green and in the process produced the gases that rusted the hands. The Hampden is a Railroad Grade watch and is in a screwed case that were designed to be air tight and dust and damp proof. This watch would originally had a thick glass crystal to withstand the robust use the watch would have been put through.

The newer type of acrylic crystals are OK and have been in use since the 1950's.

Over the years I have had quite a few pocket watches with this problem. Some of them had hands that were lightly rusted and the hands could be cleaned, polished and re-blued, but others were badly corroded and had to be replaced. All the watches had the crystals replaced.


----------



## Guest (Aug 4, 2015)

Melville said:


> The destruction of the watch hands on the Hampden is definitely caused by the chemical reactions of the polymers in these early plastic crystals that turned the plastic yellow or green and in the process produced the gases that rusted the hands. The Hampden is a Railroad Grade watch and is in a screwed case that were designed to be air tight and dust and damp proof. This watch would originally had a thick glass crystal to withstand the robust use the watch would have been put through.
> 
> The newer type of acrylic crystals are OK and have been in use since the 1950's.
> 
> Over the years I have had quite a few pocket watches with this problem. Some of them had hands that were lightly rusted and the hands could be cleaned, polished and re-blued, but others were badly corroded and had to be replaced. All the watches had the crystals replaced.


sorry to take the pi*s, it actually makes sense and is very interesting too :yes:


----------



## Melville (Jun 17, 2013)

Here are a couple of other photos of the Hampden.

The first one as I received it a few days ago, and the second one with the face cleaned. Also replacement hands and an old glass crystal from one of my parts boxes.


----------

