RetroBright Gel Ingredients
The above photo shows my own gel version of RetroBright:
• 3% Hydrogen Peroxide
• Corn Starch Powder
• OxiClean

HOW TO MAKE THE GEL

For each 50ml of 3% hydrogen peroxide (H202), I used 1/4 teaspoon OxiClean and between 1.0~1.5 teaspoons corn starch.

I started out by pouring the H202 into the small glass jar you see in the photo (which holds about 50ml of H202), then heating it in the microwave (yes, it's safe) for 20 seconds. I then took out the jar and stirred in my 1.5 teaspoons of corn starch, then I put it back in the microwave for another 20s. I then removed it, and stirred with a wooden chopstick. I then waited 5 minutes for the gel to solidify a bit, then I put the glass jar into a plastic tupperware bin (to catch spill-over). I then added the OxiClean into the glass jar and stirred with my chopstick. Beacause the mix is still hot, it bubbles quite a lot. But I found it is best to do when hot as it becomes a firmer gel later. I then went outside and applied the gell to my vintage plastics with the paintbrush you see in the photo.

WHY YOU NEED TO HEAT IT

The reason you need to heat the H202 is due to how corn starch thickens. As most cooks will tell you, you always should add the corn starch at the very end of the cooking process (otherwise the corn starch would break down due to the intense heat and not solidify your liquid), then keep it on the heat for a couple minutes and then promptly remove it. So to simulate what you get when you thicken say soup, I heated the H202 and then I added the corn starch and then I heated it slightly again. It's not as thick as you would expect, but is just enough for RetroBright deyellowing.

MULTIPLE REAPPLICATIONS NECESSARY

When doing this on a sunny day in the Springtime, you will need to reapply the gel about once an hour. That's what I did anyway and I had excellent results. (The thinking here is that when its still in gel form, the H202 will bubble and do its deyellowing job better, just as if I dipped it in the liquid version of RetroBright.) It is troublesome to do multiple reapplications all day long, so use the liquid version of RetroBright wherever you can.

WHY TO USE A PAINTBRUSH

Never forget to use a paintbrush like I did. It not only makes applying the gel easier, but you also need to scrub away some of the underlying dried gel with each new application. Otherwise, you would be applying good gel on solidified gel, and the new good gel wouldn't touch the plastic beneath.

UV LIGHT SOURCE

I have only used sunlight in my deyellowing sessions, and that sunlight was on either a sunny or partly cloudy Spring day (when UV is at it's strongest). Therefore, if you use a man-made source of UV light to deyellow inside your home, your results could vary considerably from mine. But such is only logical. Go inside your house at night at turn on some lights. Add some more light for good measure. Take note of how well lit the room is. Now wait to the following day and note how bright that same room is from sunlight coming in from the outside. Changes are the room is brighter overall (depending on how many windows you have). So even if you contend that your man-made UV light source is "stronger" in terms of UV than the sun, are you diffusing the UV from that man-made light in the same way the sun's light is diffused? In other words, are you really getting as much UV light to "various different sections of your yellowed plastic" as sunlight would? Keep in mind that I still used white reflectors when I deyellowed outside, so as to bounce the light around the object I was deyellowing. It's not just the "strength" of the UV light source. It's HOW MUCH light you can get on all sections of your plastic at the same time continually for the entire duration of the deyellowing session.

ADDITIONAL INFORMATION

You can read more about making this on the RetroBright Wiki. But keep in mind you do NOT need to use powerful H202 to get excellent results. I use 3% off the shelf peroxide and it works great. Use something stronger and you are basically wasting your money, and you also risk damaging your vintage plastics.

SEE HOW THE MIX BUBBLES IN UV LIGHT.

Read an active discussion on my deyellowing procedure in this 68kMLA thread.

And here's another 68kMLA thread that talks about my gel recipe and why you don't need highly concentrated H202.

(I am "JDW" on the 68kMLA.)

HOW TO MAKE THE LIQUID VERSION

It's basically the same as the gel recipe, sans the corn starch. For each 50ml of 3% hydrogen peroxide (H202), add 1/4 teaspoon OxiClean. Or saying it another way, for each 1.0L of H202, add 5 teaspoons OxiClean.

The amount of OxiClean you need to add is not an exact science. If you want to add a little more Oxi than I specify, it won't hurt anything. Theoretically, since it enhances H202 in the mix, it might even be better. I simply cannot speak from experience on that. My recipe is 1/4 teaspoon for every 0.05L of H202.

Best wishes to all!