Lorne,
Your experiences with Arrowroot reflect mine. Sorry about the imprecision. Peroxide is expensive and none was wasted hence I didn't "experiment" as such. The VIC-20 recipie in the blog wasn't refined. It's just what I did and it seemed to work. It wasn't necessarily the BEST way to do it. In other de-yellowings I tried slightly different amounts but I've done no trials where I've tried to alter one variable (say heating time or amount of arrowroot) keeping other variables constant.
Firstly to clear up some confusion. My microwave is 750 or 800 Watts. I couldn't find any values on the case itself but it's a small microwave, and I'm SURE it's either of those two.
Second, the quantities. I haven't measured the liquid in mm, just estimated but it's been about 1/2 to 2/3 of a cup each time. If 250-300ml is 1-1 1/4 cup then I've estimated the mm incorrectly.
Another thing, where I've found the mixture seems too thick on heating, vigourous stirring with a spoon seems to thin it a bit. On the packet it says NOT to stir it too vigourously or it will thin. Of course those instructions are for cooking where you might not want to thin it. In some cases, we might want to.
In the Vic-20 trial I talk about adding a tablespoon, then a couple of teaspoons. I've found two heaped tablespoons are fine for 1/2 - 2/3 cup. Best to make a paste with a small amount of arrowroot and solution then slowly add the rest of liquid and arrowroot while stirring with a spoon to avoid lumps.
Good idea to check it during heating. This is what I did when I did my first one, and I stopped heating once it was obviously thickened. I found it was about 45 seconds in my microwave so for subsequent de-yellowings I didn't bother to check before that time. Doing it first time, it's worth checking every 15 seconds though as microwaves vary.
Me feeling is that the H2O2 concentration should be no MORE than 6% otherwise you might get too much foaming AND it's more dangerous if it gets on the skin or in the eyes. It certainly works at 6% so my recommendation would be to dilute it to that.
I'll replace the receipe on the blog with the refined one below, showing where we are at. I think there is a lot of scope still for experimentation with qualities and heating times but from your experiences would you agree on the below..
RetroBrite paste receipe (Arrowroot varient).
Ingredients are:
- A weak solution of H2O2 at 6% concentration (dilute if necessary. Six to 12% solutions can be found at pharmacies and hairdressers)
- Arrowroot thickener (found in most large supermarkets)
- A laundry activator like Oxy or Oxi-magic (also found in supermarkets)
Wear gloves. Even a low concentration of Peroxide can burn, especially when heated.
1. Make up a 1/2 to 2/3 cup of arrowroot/H2O2 solution by gradually adding small quantities of both ingredients one at a time while stirring.
2. Heat in a microwave until the solution thickens (about 45 seconds for a 750 Watt microwave. Less for higher powered units). Do not overheat. If doing for the first time, check after every 15 seconds and stir between checks to ascertain progress.
3. Add a very small amount of Oxy (1/5 of a teaspoon). Stir into mixture. If the mixture seems too thick stir it vigourously, which will thin the mixture a little. It will foam a little but it is not explosive.
The mixture is now ready for use.
Tez