Why Do Capped Ebonite Pens Discolor At The Section?

[Downcelot]

I have some time and googling around. I come to this web and see some vintage hard rubber pens and noticed that some unrestored one lose their original black color at the section but not the body. We know that hard rubber loses color due to UV. Here is my question, if a pen is capped, how can it section lose color but not its body?

 

Thanks in advance!

[AllenG]

Wild guess here, the ink in the pen reacted with the ebonite and it affects the pen under the cap is because the cap trapped fumes from the ink allowing it to discolor the section over time.

 

Again that is speculation.

[WaskiSquirrel]

I agree with AllenG. I suspect that some of the chemicals from old inks may have discolored the pen because the cap would have held them against the ebonite.

 

But, this is a hypothesis that has not been tested.

[Lyander0012]

Hmm, either that or the section was the original colour, while the body's been subjected to restoration/reblackening.

EDIT: Whoops, re-read OP. So these are unrestored, hm? That means that the only viable hypothesis would be the ink's being the cause of discolouration. Wonder what might've been in these inks to cause it?

Edited August 30, 2014 by Lyander0012

[Uncle Red]

Washing the nib and section with warm water would do the trick, warm water causes hr to oxidize faster.

[Ted A]

Well you also have the fact that there is probably more prolonged contact with damp human fingers at the section than at the barrel. And then that damp section is closed up inside a cap so it doesn't dry as fact as the barrel

[Downcelot]

Thanks for your replies. It is pitiful that I do not have the picture now to show you. On the picture, I saw this dis-colorization on the section and a bit of the body that is close to it. There is this clear line that separates the olive/brown green bit vs the black of the rest of the body. The olive-ish bit is clearly the part that got covered by the cap. It seems the pen has been capped and abandoned for a long time.

 

I also think that trapped air environment and contamination (from hands, from inks) somehow elevate the process of losing color. It is worth while to know the exact cause. It can help us to understand, maintain, and keep hard rubber safe from dis-color.

Edited August 31, 2014 by Downcelot

[SteveE]

Hmmm. . . It could also be that the part of the barrel/section that discolored did so due to something like a chemical reaction due to the proximity of the cap to the section. In other words, this is the only portion of the pen that had ebonite covering it rather than open air. Maybe some chemical that was released by the inside of the cap caused the section and barrel inside it to discolor.

[Bo Bo Olson]

I've seen pictures where the section area stays 'black' and the barrel is turning olive green.

 

I have one, an old Mercedes where the cap and barrel are black but the hard rubber 'jewel' and piston cap have turned green.

 

So there are more than just a darker section, or lighter one.