Irregular yellowing causes: Any theories?

[ideus]

I have seen a few of irregular yellowing key caps here and there. I made a quick search and I found almost nothing on it. Does someone has any idea why the same set shows irregular yellowing? I have theorized that it may be related with the irregular use of the key caps; because, yellowing is like a superficial patina, that relates with the surface color being altered by aging agents, mainly UV rays, thus the more use the less patina added. The idea is full of black holes; for example, it does not explain a case like this Haata's specimen:





What do you think?

[suicidal_orange]

Looks like there are three distinct shades on that board (G and J, D and F, and A and S) so perhaps the caps were made from three batches of plastic with all the A's made at once rather than in sets?  Or whatever was on the hands of the person using those interesting front legends (usage pattern unknown) could be responsible, assuming haata didn't buy it new.

Unless you can find two boards used in the same place but from different batches to compare no way to tell these two apart.

[ideus]

Very interesting ideas; mainly, the possibility to compare two specimens of the same batch, however, it may be a really long shot, considering all these boards predate the eighties.

[Puddsy]

Looks like there are three distinct shades on that board (G and J, D and F, and A and S) so perhaps the caps were made from three batches of plastic with all the A's made at once rather than in sets?  Or whatever was on the hands of the person using those interesting front legends (usage pattern unknown) could be responsible, assuming haata didn't buy it new.

Unless you can find two boards used in the same place but from different batches to compare no way to tell these two apart.

I thought this was how most keycaps were made, no?

It seems to me like the best thing to do when you make keycaps in huge bulk is to make all of them one letter at a time, rather than one set at a time. That way you can save on molds, and be sure that you have enough keycaps to properly assemble all of your keyboards.

[suicidal_orange]

It seems to me like the best thing to do when you make keycaps in huge bulk is to make all of them one letter at a time, rather than one set at a time. That way you can save on molds, and be sure that you have enough keycaps to properly assemble all of your keyboards.

I were in charge I would rather do a set at once to ensure there is no colour variation, then if the materials didn't make as many as expected (SP underestimated their SA caps for years so this does happen!) only the last set would be ruined - I could sell/use 99,000 sets rather than having to hold on to 100,000 x 103 caps while waiting for the last cap of a fullsize set to be produced.  Also instead of needing 100 molds for the letter A you only need one which would make custom legends cheaper and smaller runs possible, which would be great for us enthusiasts.  As an added bonus the set would come straight off the production line ready to be packaged up with no 'sorting issues'...


I must be wrong as it doesn't work like this but I don't see any advantages to making one key at a time.


Edit:  Also saves time by not needing to swap the mold after each letter!

[keykaiser]

I would think Signature Plastics knows how to run their manufacturing line by now.

[Puddsy]

It seems to me like the best thing to do when you make keycaps in huge bulk is to make all of them one letter at a time, rather than one set at a time. That way you can save on molds, and be sure that you have enough keycaps to properly assemble all of your keyboards.

I were in charge I would rather do a set at once to ensure there is no colour variation, then if the materials didn't make as many as expected (SP underestimated their SA caps for years so this does happen!) only the last set would be ruined - I could sell/use 99,000 sets rather than having to hold on to 100,000 x 103 caps while waiting for the last cap of a fullsize set to be produced.  Also instead of needing 100 molds for the letter A you only need one which would make custom legends cheaper and smaller runs possible, which would be great for us enthusiasts.  As an added bonus the set would come straight off the production line ready to be packaged up with no 'sorting issues'...


I must be wrong as it doesn't work like this but I don't see any advantages to making one key at a time.


Edit:  Also saves time by not needing to swap the mold after each letter!

Computers have been smart enough to properly read the color of an object for years now. Just fire a laser at it and set up an acceptable margin of error for color.

EZ

[ideus]

Yellowing problem is now solved using either UV Absorbers, Quenchers or HALS plastic additives; therefore, the question was addressed more to those vintage sets that show irregular yellowing, than to sets currently in production.

[suicidal_orange]

Computers have been smart enough to properly read the color of an object for years now. Just fire a laser at it and set up an acceptable margin of error for color.

EZ

So if all your Z keys aren't the same colour as your A keys the clever computer bins them all?  That's great, but not as good as having a whole set that's a slightly different colour from the first but consistent within the set so perfectly sellable, if at a slight discount