Recently I found a parker 51, whose cap has imprint '51' in a stylized way, under it '1/10 12 cr r.gold' is imprinted.
I have a few other 51's from the middle and late 40's, but I have never seen before one with 51 on cap. So I was
wondering what is the approximate date of the pen. The pen has faint imprint on barrel, but no date code. The nib is dated 1951. Also the pen is a bit shorter than my other aeromatics, and has a very simple clip.( no blue diamond.)
Can anybody please tell the approximate date of the pen?


another question, why 1/8 14k r.gold and 1/10 16k r. gold was imprinted on caps and what do they mean?

I'm guessing you have a late Mark I US. That's when the '51' imprint and halo logo started, and the Mark IIs have a longer arrow clip. The English production late Mark I had the '51' and halo logo but the longer arrow clip.

Someone more knowledgeable than myself will be sure to come correct me. =^) I'm just looking at pictures in a book.

Let me answer what I can...
According to Ernesto Solar's Parker 51 website:
The 51 marking on the cap started in 1965
1952 was the last year that barrells were dated...

The fact that the nib is dated 1951 leads me to believe it is a replacement nib...
As for the pen being shorted than your other aerometrics, that is because it is most likely a Demi, which was a shorter pen originally introduced to appeal to the women's market. The Demi measures about 5" capped and the full size about 5.4" capped.
However, since the cap appears to be from a post 1965 pen, I think this was also replaced as the Demi was discontinued in 1961. Demi caps are also shorter than full size caps, measuring about 2.3" with the full size measuring 2.46". The cap from a full size will fit a Demi perfectly, but will look imbalanced when compared to the right cap.
You will not find blue diamond clips on any of the aerometrics. The blue diamond was only found on Parker 51 Vacumatics and was discontinued mid-year 1947

So basically what am saying is that according to your description you may have a Parker 51 Demi made up of different pen parts... not that that is a bad thing as long as the pen writes well and you did not purchase it as a collector, but as a writer.

Not that having a different date code is a problem - it's still a 51 nib.

The markings for gold content mean that one eight (1/8) or one tenth (1/10) of the weight of the cap metal minus clip, inner cap, and clutch, is gold of the content listed -- a 1/10 12k rolled gold will have gold plating thick enough to make 10% of the weight of the cap, 12k purity. If you look at the open end of some caps or barrels marked like this you can actually see the layer of gold on the base metal, although not usually on a Parker "51" as the edge is normally rolled over.

It's called "rolled gold" because in days past the layer of gold was adhered to the base metal via a hot rolling process, not electroplated. Don't know much more than that, and I would guess gold plating like this is normally electrodeposited these days.

Note that the embellishment like vertical lines are made into the gold, not the base metal, and when the gold gets worn off, the lines will almost vanish -- I have a very badly worn "51" cap in that condition. Serious brassing, too, but I didn't pay much for it.

Peter

What everyone here seems to have missed is that the cap imprint is English. US-made pens are marked "GF"; "rolled gold" was a distinctively British usage. Ditto for "CT" rather than "K" for karat/carat. English rolled gold caps bore the "51" name in the '50s. So don't assume the pen is late production, or that it is in some way mismatched.

Sorry for being not present for a few dates. First of all thank you all for the replies.
I forgot to mention the nib and barrel both are English made whereas the cap is not
imprinted the country of its origin.