Properly marked bags are less likely to end up contaminating a batch of recycling. Many products, such as compact discs, video tapes, and computer discs, are made from mixed materials which can't be recycled unless first disassembled. For clarity, a recycling symbol should be present, but most people have little trouble sorting these materials. Glass bottles must not be mixed with other types of glass such as windows, light bulbs, mirrors, glass tableware, Pyrex or auto glass. Ceramics contaminate glass and are difficult to sort out.
Clear glass is the most valuable.
Mixed color glass is near worthless, and broken glass is hard to sort. There have been marketing experiments with plastic and steel cans that look exactly like aluminum cans. Recycling plants have been damaged by these fakes. It is no longer necessary to remove labels for recycling. To save water, clean only enough to prevent odors.