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Old 9th Nov 2009, 11:20 pm   #1
Billy T
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Lightbulb Cleaning badly stained bakelite and plastic knobs

I have been trying various means of removing stains from light coloured plastic and Bakelite knobs for some time but frequently found that the stains went deeper that surface cleaning could touch. Abrasive cleaning was not much use either as it destroys the surface layer.

One day it struck me that if the stain could get in below the surface, maybe a suitable cleaning agent could to likewise, so I decided to experiment. From my collection I chose five knobs that I needed to clean and one junk knob that I thought might be beyond redemption. I then soaked them in concentrated bleach (industrial strength) and in most cases this produced an overnight miracle.

The images below illustrate five success stories and one failure.

Images 1 & 2 are before and after for two hard-to-find plastic knobs, the left hand one was in mint condition, the right hand had been either in the sun or exposed to some other ageing effect and had been pre-cleaned with a domestic spray cleaner. I soaked the stained one for several weeks

Images 3 & 4 are of a junk knob that was so bad I figured it would make a good control, and a white knob similarly stained. I didn't try any pre-cleaning at all on these two. The junk knob was soaked for two weeks but the other came clean in two days.

Image 5 is of two Bakelite or similar plastic knobs that had stains I couldn't polish out and the knob in the middle is the same type as No. 4 but without the insert. It was similarly stained orange/yellow. These were soaked for just 24 hours.

This might also work for other items of plastic trim etc, in fact I have Philips transistor fascia that I have scrubbed with cleaners to no avail, so I'll try that and report back. The bleach I used was Sodium Hypochlorite 15% which is an industrial strength version of standard domestic bleach. I believe that the same substance is used in swimming pool maintenance. It must be handled with care as it is corrosive to skin at that strength so I kept a bucket of water handy to wash off any splashes but fortunately it was not needed. It will instantly ruin clothing too!

I have subsequently experimented with warming the solution and this seems to aid penetration and speed the cleaning process. In each instance the knobs were in a capped plastic container and heating was by submersion in hot water, changed regularly as it cooled. Remove any aluminium or light alloy trim if possible, or watch closely for corrosion but I do not think this is likely to be a major problem unless soaking for longer periods i.e. weeks, not days. Pre-cleaning would definitely be advisable to expose a clean surface.

There was no ill effect on the surface of any of these knobs.

Cheers

Billy
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Old 10th Nov 2009, 5:51 pm   #2
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Default Re: Cleaning badly stained bakelite and plastic knobs

There's not a lot of point in heating any hypochlorite. All you will do is decompose it to hydroxide + chlorine. (The "bleaching" reaction is when the hypochlorite decomposes to chloride + oxygen.)
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Old 10th Nov 2009, 6:17 pm   #3
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Default Re: Cleaning badly stained bakelite and plastic knobs

I'd be extremely wary of putting any strong chemicals anywhere near bakelite. They could very easily affect the chemicals holding it together and make it very brittle.
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Old 10th Nov 2009, 11:03 pm   #4
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Default Re: Cleaning badly stained bakelite and plastic knobs

I was pondering over this earlier and noted that Billy says "Image 5 is of two Bakelite or similar plastic knobs" with specific note being taken of the "or similar" bit.

All too often we see Bakelite used as a generic term for what amounts to any rigid and old plastic. We need to be clear here regarding what is proper Bakelite and what is, in reality, a Urea type plastic. This may seem pedantic but is important when it comes to cleaning with fluids, especially chemicals such as bleach. I, like David, would be very wary indeed of showing Bakelite any form of chemical like bleach. Urea Formaldehyde yes, Bakelite no.
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Old 10th Nov 2009, 11:32 pm   #5
Billy T
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Default Re: Cleaning badly stained bakelite and plastic knobs

Quote:
Originally Posted by Darren-UK View Post
I was pondering over this earlier and noted that Billy says "Image 5 is of two Bakelite or similar plastic knobs" with specific note being taken of the "or similar" bit.
Yes, you picked it dead right Darren, I had no idea what the composition was and I've forgotten how to test (must search the forum for that, I know I've read it somewhere) so it is very much a 'user be wary' situation, but the results warranted posting for further discussion and experimentation. The most outstanding result was not the instrument knobs or even the small white examples, it was the nicotine coloured unknown plastic knob which came back to a slightly marbled look that would not be unacceptable, even as a mismatch with the unaffected sample. The good thing is you can always experiment on the underside of a knob.

Don't know about heat decomposing the bleach though, it was only warmed, not heated as such, and it didn't seem to affect it negatively at all, it was just a little more active and worked faster. I understand that Hypo is used in heated swimming pools so it must have some staying power.

Cheers

Billy

This jewellery site has interesting bakelite test info and it seems that not much true bakelite was ever produced after 1927.

http://www.vintagejewelrylane.com/in...kelitetest.htm

Last edited by Billy T; 10th Nov 2009 at 11:45 pm.
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Old 11th Nov 2009, 12:19 am   #6
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Default Re: Cleaning badly stained bakelite and plastic knobs

My understanding is that Bakelite is generally brown black and dark colours. Urea Formaldehyde , white and light colours . There are other types of plastic like casien etc.

Last edited by Darren-UK; 12th Nov 2009 at 10:08 am. Reason: Bakalite and Urea famaldahide corrected.
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Old 11th Nov 2009, 12:39 am   #7
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Default Re: Cleaning badly stained bakelite and plastic knobs

Quote:
Originally Posted by Darren-UK View Post
This may seem pedantic but is important when it comes to cleaning with fluids, especially chemicals such as bleach. I, like David, would be very wary indeed of showing Bakelite any form of chemical like bleach. Urea Formaldehyde yes, Bakelite no.
Yes, it's well known and documented that bleach (and other alkalis) will permanently wreak 'real' Bakelite.

David
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Old 11th Nov 2009, 9:45 pm   #8
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Default Re: Cleaning badly stained bakelite and plastic knobs

Quote:
Originally Posted by Billy T View Post
I Don't know about heat decomposing the bleach though, it was only warmed, not heated as such, and it didn't seem to affect it negatively at all, it was just a little more active and worked faster.
Dilute NaOCl is used in dentistry to disinfect root canals prior to placing a root filling.

I've definitely seen warming it advocated as a way of increasing its efficacy.

Nick.
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Old 12th Nov 2009, 1:53 am   #9
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Default Re: Cleaning badly stained bakelite and plastic knobs

Not sure about use on older plastics etc but this looks quite effective :-

http://retr0bright.wikispaces.com/

As a collector of old computer equipment I've kept this in mind for future use
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Old 12th Nov 2009, 11:40 am   #10
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Default Re: Cleaning badly stained bakelite and plastic knobs

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Originally Posted by chipp1968 View Post
There are other types of plastic like casien etc.
Just wondering, what is "Casien"? I thought it was something to do with cheese .
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Old 12th Nov 2009, 12:31 pm   #11
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Default Re: Cleaning badly stained bakelite and plastic knobs

Catalin, surely
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Old 12th Nov 2009, 12:54 pm   #12
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Default Re: Cleaning badly stained bakelite and plastic knobs

Casein is a protein from cows milk so Darren's comment about cheese is correct:
http://en.wikipedia.org/wiki/Casein

It can be used to make paint:
http://en.wikipedia.org/wiki/Casein_paint

And plastics:
http://www.caseino.internet-today.co.uk/social2.htm
http://www.sciencemuseum.org.uk/obje.../1981-626.aspx


PS: Found this nice DIY piece:
http://entertainment.timesonline.co....cle2537936.ece
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Old 12th Nov 2009, 12:55 pm   #13
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Default Re: Cleaning badly stained bakelite and plastic knobs

One of the easiest tests for telling Bakelite from plastic is to touch the red hot tip of a screwdriver in a place that won't show. Plastic will melt, Bakelite won't.
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Old 12th Nov 2009, 1:38 pm   #14
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Default Re: Cleaning badly stained bakelite and plastic knobs

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Casein is a protein from cows milk so Darren's comment about cheese is correct... It can be used to make... plastics...
Fascinating, Jeffrey.
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Old 13th Nov 2009, 5:16 am   #15
Billy T
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Default Re: Cleaning badly stained bakelite and plastic knobs

Quote:
Originally Posted by David Tilley View Post
One of the easiest tests for telling Bakelite from plastic is to touch the red hot tip of a screwdriver in a place that won't show. Plastic will melt, Bakelite won't.
There is no real difficulty at all in distinguishing Bakelite from other 'plastics', the feel, weight and scratch resistance should sort that out quick-smart and I think most people could also pick the difference from colours and flexibility. However, Bakelite is also by definition a plastic, so there is nothing to distinguish in that regard anyway. What we need to be able to do is distinguish the different types of thermosetting plastics and that gets a bit problematic given that the variants all seem to be based on formaldehydes differing only in the chemical composition of the mix and the presence or absence of fillers.

I found the following description on a site discussing mah jong tiles:

1. How to tell the difference between Catalin and Bakelite?

Bakelite and Catalin are both trade-names for early thermosetting plastics based on formaldehydes. Bakelite was manufactured by a US company, Catalin was manufactured in direct competition by a UK company. Actually the trade-names covered a range of different plastics such as phenol formaldehyde, urea formaldehyde and melamine formaldehyde and don't refer to a specific compound.

To complicate things further each of these plastics could be compounded differently by adding (or not adding) certain additional ingredients (called 'fillers' in the business, carbon black being the stereotypical example, added to increase strength and lower cost, but resulting in a darker coloured material). Right from the start plastics were tailored to a certain degree to get the kind of properties and cost wanted.

However, there are some general differences as follows:

Phenol formaldehyde is always relatively dark in colour, usually dark orange, tan, brown or black.

Urea formaldehyde is usually lighter than phenol formaldehyde, often yellowish-white, a bit softer, and was a popular 'fake ivory'.

Melamine formaldehyde is usually quite a bit lighter, translucent, and harder.

Our feeling is that if it is phenol formaldehyde it is more likely to have been sold under the Bakelite trade-name, if it is urea or melamine formaldehyde it is more likely to have been sold as Catalin, but at the end of the day the names are virtually interchangeable!


I found that illuminating, not least because a family radio from the '60s may actually be Catalin, because there are no fillers and the dial lamp shines through the top of the cabinet, but it is still bakelite.

There is an excellent eBay FAQ on the subject as well, which acknowledges wikipedia as its source so that is worth a look too.

Cheers

Billy

Last edited by Billy T; 13th Nov 2009 at 5:32 am.
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Old 15th Nov 2009, 1:31 pm   #16
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Default Re: Cleaning badly stained bakelite and plastic knobs

I have found something called "Bar Keepers Friend" most effecacious for Bakelite and knobs, especially when applied with a toothbrush. Available from Wilkinsons and the like.
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