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Old 12th May 2019, 12:08 pm   #1
G3VKM_Roger
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Default Discolouring of a GPO 746 phone?

Hi All,

I recently acquired a 746 telephone and have a question on possibly removing discolouration of the outside surfaces. I have attached a photo which I hope will show the problem.

The bulk of the outer surfaces are an "ivory" colour but the area underneath the handset and the face of the handset that is downwards when "on the hook" is white. I suspect that the phone was used in a environment where there were heavy smokers and was originally white all over, although there is no smell of smoke. Another thought, is discolouration by strong sunlight a possible cause?

Is there a surface cleaner that members could recommend or is this discolouration not removable without damaging the surface?

Thanks

Roger
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Old 12th May 2019, 12:42 pm   #2
ajgriff
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Default Re: Discolouring of a GPO 746 phone?

UV I'm afraid. Looks like the back of the phone was close to a South facing window. Might be improved, but probably not eliminated, by plastic polishing and a lot of elbow grease. I use cerium oxide but any good quality plastic polish should help. Much depends on the depth of the chemical change.

Alan
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Old 12th May 2019, 1:31 pm   #3
ThePillenwerfer
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Default Re: Discolouring of a GPO 746 phone?

It's simply the effect of aging on ABS which is exacerbated by UV light.

As said, the only answer is removing the damaged top layer of plastic, like cutting paint back on a
car.

Brasso, T-Cut and the like will do it at length but I start with 500 grit wet and dry and work up to 2,000 before using liquid polishes.

There's also the technique of "Chemical Sanding." This involves rubbing it with acetone, which melts the top of the plastic. You then switch to a 50:50 mix of acetone and meths as this is less vicious so leaves a smoother finish.

The Retr0bright (sic) method is another option but buying the stuff to do that would probably cost as much as a new case.
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Old 12th May 2019, 2:48 pm   #4
vic0239
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Default Re: Discolouring of a GPO 746 phone?

I've had great success by using a solution of "OxiClean" dissolved in a basin of hot water. Place the discoloured pieces in the water and leave outside in full sun for an hour or so. Turn occasionally to make sure every side is exposed at some point. Stubborn discolouration will take longer. Once rinsed and dried the parts will polish to a wonderful shine.

NB This method works well on lighter coloured plastic, but extra care is needed with dark colours which are prone to blooming which will require some elbow grease to remove!
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Old 12th May 2019, 3:24 pm   #5
BRASSBITS
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Default Re: Discolouring of a GPO 746 phone?

Quote:
Originally Posted by G3VKM_Roger View Post
Hi All,

I recently acquired a 746 telephone and have a question on possibly removing discolouration of the outside surfaces. I have attached a photo which I hope will show the problem.

The bulk of the outer surfaces are an "ivory" colour but the area underneath the handset and the face of the handset that is downwards when "on the hook" is white. I suspect that the phone was used in a environment where there were heavy smokers and was originally white all over, although there is no smell of smoke. Another thought, is discolouration by strong sunlight a possible cause?

Is there a surface cleaner that members could recommend or is this discolouration not removable without damaging the surface?

Thanks

Roger
I could be wrong but I have never seen a white 700 series only in cream / ivory
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Old 12th May 2019, 3:43 pm   #6
G3VKM_Roger
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Default Re: Discolouring of a GPO 746 phone?

Many thanks chaps,

A few ideas to try out. I think the "natural" colour is ivory and I've established that smoking wasn't an issue, so the white patches may well be UV.

All the best,

Roger
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Old 13th May 2019, 10:30 am   #7
ajgriff
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Default Re: Discolouring of a GPO 746 phone?

Quote:
Originally Posted by vic0239 View Post
I've had great success by using a solution of "OxiClean" dissolved in a basin of hot water. Place the discoloured pieces in the water and leave outside in full sun for an hour or so. Turn occasionally to make sure every side is exposed at some point. Stubborn discolouration will take longer. Once rinsed and dried the parts will polish to a wonderful shine.

NB This method works well on lighter coloured plastic, but extra care is needed with dark colours which are prone to blooming which will require some elbow grease to remove!
I'm no chemist but I think OxiClean is effecively a bleach since hydrogen peroxide is produced when it's dissolved in water. This would explain the blooming which would be more obvious with darker colours. The polishing required after treatment would remove the bleached surface. My initial thought would be that you might as well miss out the bleaching phase and just polish/abrade from the start. Borax is a cheaper alternative to OxiClean by the way.

Alan
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Old 13th May 2019, 1:22 pm   #8
vic0239
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Default Re: Discolouring of a GPO 746 phone?

That's more than likely correct, but in my experience the colour of the plastic once dried is pretty much like the original unblemished parts. I use Greygate Plastic Polish which is less abrasive and gives a smooth deep shine. BTW the OxiClean came at no cost (to me) as I discovered it amongst the cleaning paraphernalia under the sink!
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Old 13th May 2019, 2:19 pm   #9
ajgriff
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Default Re: Discolouring of a GPO 746 phone?

Really like your trimphone and it has polished up very well after cleaning. When the free OxiClean runs out you'll now be able to save a few pennies by buying borax instead.

Alan
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Old 19th May 2019, 11:25 am   #10
DKD Contempra
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Default Re: Discolouring of a GPO 746 phone?

I took my yellowed white Northern Electric 10 button 1554 and soaked it in some peroxide and warm water in the sunshine. Started around 10:00am and finishing up at 4:30. It wasn’t too bad considering the clouds covered the sun every now and then. Had it been sunny all day it would have taken less time.

Just soaked it in 1 part 20% peroxide and 4 parts warm water in the sunshine for about 6 1/2 hours. In this case 4 Gallons of warm water (15.12 L) to 1 Gallon 20% peroxide (3.78 L)

Make sure you wear rubber gloves when working with this mixture.
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Old 19th May 2019, 2:36 pm   #11
Dave Moll
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Default Re: Discolouring of a GPO 746 phone?

Just to clarify, those are American gallons. The imperial equivalents are 0.83 gallons peroxide to 3.33 gallons water - but of course the proportions of 1:4 are still the same!
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Old 19th May 2019, 4:13 pm   #12
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Default Re: Discolouring of a GPO 746 phone?

I'm impressed by that result!

But also confused.
Is the glass tank a means of keeping the solution warm for free, or does UV help the bleaching process?
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Old 21st May 2019, 5:07 pm   #13
vic0239
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Default Re: Discolouring of a GPO 746 phone?

I think the UV plays a large part in activating the peroxide, so the tank will allow better coverage of the items inside.
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