#1 Science Forum For Lab Technicians

What concentration do you use for Methylene Blue? I have 1% at the moment but some teachers say it is still too dark.

It's only for junior students dying onion cells.

Have you got a copy of The Laboratory? (If not get hold of one!) I can't remember what I used and too lazy to walk to Science to check. But pretty sure I had a 10% stock solution that I diluted down to 1% when needed. It does degrade over time. Maybe make a new batch?

That sounds like the stock solution which you then dilute down to 1:10 with distilled water. Try 1ml methylene blue solution in 9ml distilled water and see if it still works.

I use a 0.1% concentration for Methylene Blue and it works really well, and has been in vials since 2006.