If your question isn't answered here, comment and I will try my best to answer it.
Where do I buy Hydrogen Peroxide?
H2O2 can be found in many places. Your local drug store will probably carry a 3% solution. Larger percentages can be found at beauty supply stores. Sally's is a worldwide chain and it is where I get mine. Remember to only get the "clear" kind and NOT "cream". Also 10 volume = 3%, 40 volume = 12%.
Does this only work on White?
No. I have had success using this on blue, old gray, and trans clear. I will warn you though, blue and old gray need to be watched. If left in too long the will become bleached. Or as the guys on Retr0Bright call it "bloom". So be careful with blues and old grays.
Will this fade printed bricks?
Usually No. If the printing is in good condition it should hold up to the process. If the printing is all ready faded or worn it may suffer more fading. All my printed parts have turned out ok. My suggestion is to test this for yourself.
Does the solution last forever?
No. Once the Oxy detergent has been mixed in with the H2O2 the process has started and the Hydrogen is being depleted. Once all the Hydrogen is gone, it will no longer work.
Why leave it in the Sun? Isn't it what started the whole thing?
True, the UV light made your parts turn yellow. But the UV light is what makes this process reverse itself. The UV light gets the Bromine atoms excited again but this time instead of oxygen we are force feeding it hydrogen. See next question.
How does this work?
LEGO bricks are made from ABS plastic. A common chemical found in ABS from the 80's to late 90's is Bromine. Bromine is a flame retardant and its natural color is brown. UV light degrades Bromine and it attaches to oxygen atoms. These brominated chemicals start to move around in the plastic, usually coming to the surface, and show their natural brown color. The solution and UV light break down these radical Bromine atoms and replace the unstable oxygen atom with a more stable hydrogen atom. That was the really brief explanation, for a more scientific one head over to Retr0Bright.
Why use Gloves?
Hydrogen Peroxide can burn your skin. Using plastic gloves will protect you and allow you to work more easily with the solution.
Is it bad if the LEGO is floating?
Kind of. Try your best to submerge all the parts and get rid of any air bubbles. Toothpicks work wonderfully there. If the solution isn't touching the plastic it won't work. So if it is out of it, nothing will happen.
Will this Oxy detergent work?
My advice is to check on Retr0Bright. They have tried many different brands and have answered this question many times over there.
How much does this cost?
Not a lot. 950ml of H2O2 is less then $6 and the Oxy detergent (which my wife all ready uses so we have it) is less then $10.
My part is taking forever, is it working?
Weaker H2O2 (3%) will take longer then stronger (12%) ones. Also if the part is really yellow, it will take longer. I have noticed that the thinner the plastic the faster it goes. So an old Pirate Flag will take less time then a 2x8 Brick.
Can I leave this going over night?
Yes. If you are using a UV lightbulb feel free to keep this going. If you are just using the sun not much will change in the dark. Remember to watch blues and old grays.
Are these bricks now immune to UV?
No. These bricks are not immune to UV. They can get yellowed if left in UV light. So please take care of your LEGO.