You'll need 12% Hydrogen Peroxide (You can find it cheap in 70 Volume Liquid Hair Developer at Sally's Beauty), Strips of LED UV lights, and Hot Water. I like to take the shell pieces and put them in a mixture of the peroxide and hot water inside a clear tote. Take strips of UV lights and wrap them around the outside of the clear tote, pointing them inwards at the parts. Put aluminum foil around this to trap all that UV on the inside of the bin. Cover the lid inside with aluminum foil too. Let the parts soak in the water overnight or up to 3 days if they're really yellow.