Over the past two weeks I made 12 batches of the paste/gel, and used them on a bunch of different computer parts.
I varied the quantities of Xanthan Gum used, and the mixing order/durations.
After nine variations, I found a recipe I liked the best, and used it for the last three batches. The last batches were successfully duplicated using the exact same ingredients and mixing durations. It’s not so gooey that you can’t brush it on, but it’s sticky enough that it will hold on vertical surfaces. Some of the other mixtures I tried were so gooey that I had to use a putty knife to spread the stuff. Mixing durations have a marked effect on the consistency of the paste/gel.
I used this small Hamilton Beach hand drink mixer – model # 51101B ($ 15 at Wal-Mart).
It’s the perfect size for mixing a 200 ml (almost a cup) batch, which is about as much as I’ve ever had to make at one time. I tried mixing a 100 ml batch, but it doesn’t mix as well at that quantity. I’m using the metric ml measurements as they can’t be confused, like pints or gals (eg: Imp vs US gal).
Things I’ve learned:
I’ve found that using both arrowroot and the powdered hair bleaching product that I’d tried before, makes a whiter paste gel, rather than the clearer paste/gel that I get using the Xanthan Gum. (Maybe I mixed the arrowroot version too long or not long enough). In any case, I found that both the arrowroot and powdered bleach versions dried out too quickly and formed an outer “crust”, requiring more applications. The Xanthan Gum version forms a very thin outer film, but it’s almost transparent, and I believe it’s still allowing the UV to penetrate. It also seems to take longer to dry out, which is probably the result of using glycerin in the mix.
Source of UV:
While using the sun as a source of UV doesn’t cost anything, there are some benefits to using artificial UV such as black light bulbs.
I used black lights in my garage, and this provided a much more controlled environmental condition than the outdoors. Outside, you have to contend with the weather – one minute the sun can be full strength, and the next minute it can be behind the clouds (not to mention rain – although not a problem where I am). In addition, there can be wind or a slight breeze outside which causes the mixture to evaporate and dry out too quickly, requiring additional applications of the paste/gel. That doesn’t happen in the garage (unless it’s summer and I turn on the garage A/C unit).
The black lights provide the same amount of UV to the areas being processed, at all times – the sun moves, so sometimes you’ve got parts of a piece in the shade, and other times you’ve got parts in the sun.
The black lights don’t generate anywhere near as much heat as the sun can. In full AZ summer sun, the parts & paste/gel get very hot.
As an added benefit, any small flies that happen to be in your garage, are attracted to the bubbling mixture being illuminated by the black light, and get stuck to the mixture thereby ridding your garage of the flies. (the five black spots are the flies)
Other things:
IBM plastics don’t seem to have yellowed as bad as some other (like Osborne) plastics do. The plastic even feels different (thicker & heavier). Must have been a better quality plastic or had less flame retardant in it. (Merlin ?)
In any case, they still de-yellow fine – there’s just less difference to notice.
Parts being de-yellowed can’t be made to be any more white, grey or beige than they were originally, no matter how many times they are processed.
EDIT: Except black or dark blue plastics - do not try to de-yellow these - more experimentation needs to be performed.
If you want to know what the original color was, so that you de-yellow long enough to get back to that original color, pull of a label. It’ll give a great indication of the color you are trying to get to.
I’ve processed some parts for not long enough, and later found that the color was not as de-yellowed as much as it should have been. Or, you can just leave the parts de-yellowing for two or three times as long because they won’t get too de-yellowed. I prefer to monitor the color for time reasons (I’m impatient), and to reduce the number of applications required.
Some problems and pitfalls:
Do not use a sticky tape such as brown packing tape on painted metal badges/stickers – it will pull the painted logo or name off the metal.
Do not brush the paste/gel over a painted metal badge/sticker – it will remove the paint. You should remove the metal and any other badges/stickers before processing the piece. Most of them are just stuck on using two sided tape or a contact type cement – you can get under the edge of them with a single edged razor blade or an X-Acto knife and gently pry it off. They can be re-attached later with a good quality glue such as 3M Super 77 Multipurpose Adhesive.
As an experiment, I tried mixing different ingredients at different times. Do not mix the glycerin with the H2O2 first – the order that the ingredients are mixed in, is as important as the mixing durations. If you mix the glycerin and H2O2 before adding the Xanthan Gum, the mixture is so slippery, that after 5 minutes of trying to get it to stick to a part of the plastic, any part of the plastic, you’ll want to go get the sledge hammer. It just moves around on the plastic, like an ice cube on a sheet of glass in the sunshine.
I have had one piece of plastic that I couldn’t process the way I would like. It was an Osborne case. The Osborne case has two halves. One of the halves processed back to its original color, matching all the other pieces from the same computer. The other half however, will not, even after processing it four times, get back to the same color as the other pieces. It’s a different shade of grey. I don’t know if this is because it came from a different batch of plastic, which seems unlikely because it would have probably looked different before it yellowed, or if someone switched the case half with a less yellowed half at some earlier point in its life. I suspect the latter.
THE Recipe:
Ingredients:
200 ml H2O2 (30% solution used)
2 level tsp Xanthan Gum
1 level tsp Glycerin
1/4 level tsp Oxy laundry detergent powder
1 tsp hot (not boiling) water
Process:
In a very small ceramic or plastic bowl/dish, dissolve the Oxy in the hot water (I found that the Oxy doesn’t want to dissolve in the paste/gel very well – this fixed that problem).
While that is dissolving, mix the H2O2 and Xanthan gum in the blender for five seconds (and not five or ten, just five – got it Merlin?).
Add the glycerin to that mixture and blend for another five seconds.
Let this mixture sit for five minutes.
Blend for another five seconds.
Thoroughly stir in by hand, the dissolved Oxy/water mix.
This will provide a sticky but brushable mixture with a good consistency that will stick to vertical surfaces but won’t be too gooey. Using a different blender than the one I used will probably provide a different consistency, and you may need to experiment with mixing times/durations.
Keyboard key caps will need to be processed in a liquid mixture of H2O2 & Oxy. It is not practical to process these items with the paste/gel. (Merlin: need to add that to the Wiki?)
Some photos will follow in a couple of weeks, once everything has been put back together.
