Bleaching Woodstocks and Topcats

[PANAMATIK]

Everybody knows, that the plastic cases of many calculators are sensible to sunlight and get brown over the years. After having found an interesting website about bleaching with Hydrogenperoxide I tried to bleach my HP97.



I made these two photos, one before and one after a two day bleaching, for comparison both with a normal grey woodstock case on the left. But I was very careful and didn't bleach very long and used only 3-6% H2O2, thus I added some water.

Sunlight or UV light accelerates the bleaching process, but is not necessary if you have time.

For needing less liquid to cover the big HP-97 case, I added glass marbles, to rise the surface level. It does not have any chemical influence.



The ugly brown color is now grey again and looks much better than before, however my results are not perfect, because some parts became a little patchy, but this is even more visible on the photo than in real. I think this effect can be minimized, if the case is cleaned very well with a fat solvent before the procedure. Or it will vanish after extensive bleaching with high concentrate 30% H2O2 until the case is completely light grey. I did not yet test this approach.

But experiments shall be continued

Bernhard

[Dave Frederickson]

I was looking into Retr0bright a while back. There are several forum members who have used this technique.

[PANAMATIK]

(06-23-2015 08:20 PM)Dave Frederickson Wrote:  I was looking into Retr0bright a while back. There are several forum members who have used this technique.

I read about Retr0bright. They use also hydrogenperoxide but have accelerated the bleaching process by an additive catalysator. What I don't know is whether their results show also the problem with irregular bleaching. Did anybody experiment with it?

Bernhard

[Dave Shaffer]

If you haven't done so, you should probably agitate your H2O2 solution from time to time (try rocking the container around). You may be using up the "bleaching power" in some spots. Especially with your marbles (a really slick idea!), there is probably very little circulation of the liquid.

[PANAMATIK]

(06-23-2015 09:17 PM)Dave Shaffer Wrote:  If you haven't done so, you should probably agitate your H2O2 solution from time to time (try rocking the container around). You may be using up the "bleaching power" in some spots. Especially with your marbles (a really slick idea!), there is probably very little circulation of the liquid.

The phenomenon of irregular bleaching is well known by others, who tried that. It is not caused by the marbles, because I had the same effect also with the smaller woodstock cases, for which I didn't need marbles. Also I did circulate the liquid from time to time.

Bernhard

[BobVA]

(06-23-2015 10:12 PM)PANAMATIK Wrote:  The phenomenon of irregular bleaching is well known by others...

Just guessing here: Is it possible that it's a result of surface preparation prior to bleaching? Would cleaning the case with a good detergent, followed by a rinse in distilled water and handling with gloves, perhaps help?

Interesting experiment!

Bob

[Geoff Quickfall]

I tried a wood stock, firstly scrubbing with soap and water, then a domestic ammonia product.

Let it sit in dilute household bleach for seven days agitating daily. This resulted in a patchy finish. Another ammonia wash, rinse and a diluted hydrogen peroxide bath for three weeks again agitating and sitting on a window sill under full sunlight.

After drying it still had a mildly patchy finish albeit better then belch alone. I gave up, maybe the patches are part of the manufacturing process?

Geoff