hp 28s yellowed keys.

[Rafa]

I recently got an hp hp 28s and noticed straight away that the keyboard is darker than how this model appeared in photos and videos.
the white keys are yellow, the shift button is so dark it is closer to reddish purple than the rich red color i see on other hp 28s, even the plate of the keyboard seem darker und duller.

I'm wondering if this is the effect of the chemical reaction of UV and the fire retardant bromine that was used in plastic in those old days, or a production batch that used a darker hue?
Although yellowing as a chemical reaction is the more likely explanation, i included the second possibility just because, to my eyes, the darker appearance of the calculator is consistent throughout, i.e the plates, grey keys, cream keys, and red shift key are all harmoniously of a darker tint.

It is not a big drama for me but rather a small disappointment as i wanted to have the 28s, in small part, because the overall look and the combination of the rich red, light cream, and grey color scheme of the keys made for a very attractive and visually pleasant aesthetic (to me at least).

Is there a safe way to brighten up the keys and restore them to their original tint without having to dismantle the calculator?

Thanks!

[Maximilian Hohmann]

Hello!

(05-30-2024 06:39 AM)Rafa Wrote:  Is there a safe way to brighten up the keys and restore them to their original tint without having to dismantle the calculator?

Maybe with ozone, but who knows what this will do with the rest of your calculator. From your picture (taken with a phone?) it is not really obviuos to me what wrong colours you see in your calculator. The purple shift key looks perfectly normal to me, the bright red ones shown in some photographs are not what the calculator really looks like!

Right now I only have an HP-28C on my desk for comparison, but its white keys are not really white either, rather something between beige and light grey. I will attach a photo of that calculator below that I took on a white sheet of paper for white-balancing in a graphics program.

Regards
Max

[Rafa]

(05-30-2024 05:30 PM)Maximilian Hohmann Wrote:  Hello!

(05-30-2024 06:39 AM)Rafa Wrote:  Is there a safe way to brighten up the keys and restore them to their original tint without having to dismantle the calculator?

Maybe with ozone, but who knows what this will do with the rest of your calculator. From your picture (taken with a phone?) it is not really obviuos to me what wrong colours you see in your calculator. The purple shift key looks perfectly normal to me, the bright red ones shown in some photographs are not what the calculator really looks like!

Right now I only have an HP-28C on my desk for comparison, but its white keys are not really white either, rather something between beige and light grey. I will attach a photo of that calculator below that I took on a white sheet of paper for white-balancing in a graphics program.

Regards
Max

Hi max,

thanks for answering. i did take the photo with a phone and made few attempts to capture the colours as the are but the results were always way brighter, which made me think that possibly all these other hp 28s in photos or in youtube videos are also being brighten up by the lens? the photo i uploaded was taken in a darker room and the result was still brighter than the real colours!

i'm aware that the numerical keys are actually cream rather than white and the shift key is kind of dark red, but the reason i'm suspecting mine is unusually dark is that the cream keys have a clear yellowish tint to them and the shift key is crimson red, which is not that bad. it is the yellowish keys that give me an eye sore. i definitely am not so bothered that i'd try some risky chemical sorcery. I thought that if this was an easy rub with something that one can buy in Rossmann and does not seep into the electronics then i might consider it.
I guess if you did manage to capture the real colours of your 28c then from what i see mine is definitely duller and darker.

i think i will just have to see another device to compare it side by side with mine.

many thanks again for the reply and the photo!

[Maximilian Hohmann]

Hello,

(05-30-2024 06:31 PM)Rafa Wrote:  i definitely am not so bothered that i'd try some risky chemical sorcery. I thought that if this was an easy rub with something that one can buy in Rossmann and does not seep into the electronics then i might consider it.

The only substance that comes to mind, apart from ozone which I already mentioned (*), is hydrogen peroxide cream oxydant. Rossmann probably does not have it, but you can mail order it from Amazon. I have seen it recommended for whitening computer keyboards that have turned yellow over time. It is a gel that can be applied to the keys with a cotton swab and which won't seep into the calculator. But you might want to try it out with another, possibly non-functioning, calculator first!

Regards
Max

(*) Applying ozone is not as scary as it sounds. I have been using a little ozone generator since years for variuos purposes. They can be found on eBay/Aliexpress for very little money but the cheap ones are probably not compliant with European standards regarding electrical safety. Put it in a plastic box together with the object you want to treat, place it somewhere outside of your appartment (ozone is good for the stratosphere but not for our lungs) and let it run for some minutes. The only thing I ever ruined with ozone was a pair of sport shoes of my son. They were not as white any more as he wanted them to be. The ozone restored the colour, but the plastic or rubber of the sole turned so brittle that it broke into pieces when he tried to put them on.

[Rafa]

(05-30-2024 08:58 PM)Maximilian Hohmann Wrote:  Hello,

(05-30-2024 06:31 PM)Rafa Wrote:  i definitely am not so bothered that i'd try some risky chemical sorcery. I thought that if this was an easy rub with something that one can buy in Rossmann and does not seep into the electronics then i might consider it.

The only substance that comes to mind, apart from ozone which I already mentioned (*), is hydrogen peroxide cream oxydant. Rossmann probably does not have it, but you can mail order it from Amazon. I have seen it recommended for whitening computer keyboards that have turned yellow over time. It is a gel that can be applied to the keys with a cotton swab and which won't seep into the calculator. But you might want to try it out with another, possibly non-functioning, calculator first!

i've looked up the hydrogen peroxide and saw a video with impressive results! probably the gel form will be less messy than the cream version, there was just the issue of applying it thoroughly and in generous amount on the surface of the plastic otherwise there is a risk of streaky result, by which i understood an inconsistent de-yellowing.
and since i can't take the keys out i'm a bit nervous about the "generous amount" of the stuff that needs to be somehow "rinsed" away afterwards and dabbing might push the stuff inside through the gaps around the keys... but yeah i could try it on a cheap old calculator first.

that disintegrating shoes must have supplied your son and his friends with some amusement : ) luckily shoes are very much replaceable!

have a nice weekend!

[Bernd Grubert]

Hello,
There was an article in German on heise.de about the restoration of vintage computer housings and keyboards. It describes the reason for plastics becoming yellowish (UV-light) and compares the different methods for bleaching. Unfortunately it is behind a paywall. But if you're interested, here is the link:

https://www.heise.de/ratgeber/Aus-Gelb-w...?seite=all

[Rafa]

(05-31-2024 06:32 AM)Bernd Grubert Wrote:  Hello,
There was an article in German on heise.de about the restoration of vintage computer housings and keyboards. It describes the reason for plastics becoming yellowish (UV-light) and compares the different methods for bleaching. Unfortunately it is behind a paywall. But if you're interested, here is the link:

https://www.heise.de/ratgeber/Aus-Gelb-w...?seite=all

Hi Bernd,

thanks for the link. from what i read elsewhere, in old plastic, a flame retardant chemical called Bromine was added to the mixture. Over time and with long exposure to UV the molecules of this chemical broke down and escaped to the surface of the plastic causing the yellow tint. some people discovered that hydrogen peroxide in 12% concentration found in a cosmetic product can de-yellow the plastic by applying hydrogen peroxide onto the plastic and, ironically, exposing it to sun light for a day or two!

i'm not sure if that's the same method the german article describe. i will see if it's worth paying to read it.

thanks for the tip.

[vaklaff]

Retrobright is the term you may want to look up. I’d suggest videos from a fellow forumer - channel Hey Birt! I could spend days watching his work, amazing!

However applying retrobrighting on a 28’s keys is only for the very brave, simply because taking the calc apart is hard and putting it together in good cosmetic condition is next to impossible…

I wouldn’t worry too much about the colors. Instead, enjoy the machine while it works.

Just my 2 cents

[Dave Frederickson]

(05-30-2024 06:39 AM)Rafa Wrote:  Is there a safe way to brighten up the keys and restore them to their original tint without having to dismantle the calculator?

A safe, easy thing to try is a Mr. Clean Magic Eraser or melamine sponge. No chemicals or disassembly required. My results varied.

[Rafa]

(05-31-2024 10:51 PM)Dave Frederickson Wrote:  

(05-30-2024 06:39 AM)Rafa Wrote:  Is there a safe way to brighten up the keys and restore them to their original tint without having to dismantle the calculator?

A safe, easy thing to try is a Mr. Clean Magic Eraser or melamine sponge. No chemicals or disassembly required. My results varied.

i think this one works by shaving a bit of the surface that is stained. Also the surface here is not flat for a solution like a melamine foam.
thanks for the tip, though

[Rafa]

(05-31-2024 06:59 PM)vaklaff Wrote:  Retrobright is the term you may want to look up. I’d suggest videos from a fellow forumer - channel Hey Birt! I could spend days watching his work, amazing!

However applying retrobrighting on a 28’s keys is only for the very brave, simply because taking the calc apart is hard and putting it together in good cosmetic condition is next to impossible…

yeah taking it part is out of the question. There's a hair dying product that contains the hydrogen peroxide used in retrobrighting and it comes in gel and cream forms. I think i will look into the gel stuff to find out if i could apply it directly onto the keys and then have it somehow removed without risking any of the stuff getting into the calculator through the gaps around the keys.

but yeah it's not a big deal, if it's not 100% safe then i won't do it.

[rprosperi]

My opinion, which likely is no help at all is this: If feeling that your unit, which may be slightly darker than a typical unit, bothers you, then I think the result of any chemical treatment, which will inevitably produce inconsistent / uneven coloration, would really, really bother you.

Maybe just think of your unit as a "rare, slightly darker-themed HP-28S" and take comfort in knowing it's a rare model with unusually even colored aging?

Published results of such chemical treatments typically only produce good, even color lightening on large, flat, even surfaces, and is almost certain to have uneven results on such a complex surface as 50+ keys, bezel, etc. And that's a best case scenario if the chemicals don't do any internal damage.

As I said, likely not helpful....

[Rafa]

(06-01-2024 11:04 AM)rprosperi Wrote:  If feeling that your unit, which may be slightly darker than a typical unit, bothers you, then I think the result of any chemical treatment, which will inevitably produce inconsistent / uneven coloration, would really, really bother you.

hehehe, yes my thoughts too. i'm only ever so slightly bothered by the yellowish tint but on the other hand an uneven coloration or streaky results would definitely be much hard to get over.
I was already leaning on the conclusion that this is just its age and part of it.
and actually the board inside my head discussing this topic was overwhelming majority in favour of not doing anything. and just to try to convince this one single board member who wanted to at least find out more, i went ahead and wrote in this forum about it to have more people weighing in. so your opinion, along the others, was also very helpful : )

[Maximilian Hohmann]

Hello!

(06-01-2024 12:36 PM)Rafa Wrote:  I was already leaning on the conclusion that this is just its age and part of it.

Part of it certainly, but the age alone does not cause yellowish coloration of the keys, as you can see in the picture of my (older) HP-28C above.

One "simple" solution could be to look for another HP-28S which pleases you more and resell yours. With a bit of patience this should be possible without losing a lot of money. They have become quite rare but occasionally one pops up for a reasonable price. I bought the 28C above two years ago on eBay with fresh batteries and printed manual for 10 Euros. There are still bargains out there :-)

Regards
Max

[Rafa]

(06-01-2024 02:23 PM)Maximilian Hohmann Wrote:  Hello!
I bought the 28C above two years ago on eBay with fresh batteries and printed manual for 10 Euros. There are still bargains out there :-)

10€ is not just a bargain, it is practically a gift! : )

[Rafa]

it turns out there was a different unit that had this brighter appearance. units made in the US, like mine, had the darker tint and in the last year or two of production the 28s was made in Singapore and had lighter colours throughout, also had a different screen.

i found a picture of someone's collection, he had 4 hp 28s, 3 of which were made in the US and all three were identically of this darker tint while the fourth looked different and is made in Singapore, they were also optimally laid on top of each other which makes the contrast between them very clear to see.

Thought it might be of interest to someone since this difference has not been pointed out.

the photo is attached.