I heard one can add bleach in washing machine in order to lighten the colour of a pair of jeans. Could I make the colour of the jeans on the right just like the colour of the jeans on the left using that method, and if so, how much bleach should I use? Should I add some washing powder too or just bleach?
Yes, you can if I am understanding.
Putting Bleach in your washer is not the method. This will bleach the whole jeans and probably do it unevenly.
This is the method: http://m.wikihow.com/Bleach-Jeans
Get a 1 to 3 bleach solution and carefully apply in the pattern you want. Apply by spray bottle, sponges, or painting. Whichever you want and is better for the design. Tie off the areas you are not doing and wrap those in plastic wrap or bags. Not Neccesary, but I am very careful. Bleach cannot be undone. Wash the jeans after, but be sure to rinse the area with bleach to get most of it out before washing them so the whole jeans don't get bleached. Try doing at least 2 or 3 treatments, so you can go slow and do not try do in it all at once just in case you do much and ruin them. For the design your going for I would say at least 2 sessions and a sponge.
If misunderstood you and you want to lighten the whole jeans I would say: http://www.mademan.com/mm/how-fade-jeans-home.html
Put about a pint and a half in your washer and let that site for about 20 to 30 minutes.
Start the washer again.
You can always do extra sessions. So to much can be much.
Note: Some say Bleach pen. But that can look really "unnatural". I reserve that for lettering and bleaching emergencies :)
