Paper labels may be left on containers. To protect yourself and workers at recycling centers, take care not to break glass containers you collect. Glass plants have found increasing the percentage of scrap container glass, or cullet, in their manufacturing processes saves on maintenance and energy. However, glass plants have certain quality standards Recyclers should know to receive the best prices for cullet. Other materials that cannot be recycled with glass are mirrors and most drinking glasses.
Contaminants can seriously damage the furnace or result in poor quality of the plant's product.
Glass furnaces operate at temperatures of up to 2800 F. Lead and aluminum melt at this temperature while iron and lead settle to the bottom of the furnace tank and corrode its brick lining. Stones and seeds can be deposited in the walls of the glass containers being made, causing aesthetic problems and weakening the bottles wall. Steel lids also do not melt at furnace-operating temperatures. As a result, they sometimes block feed lines going from the furnace and cause production shutdown. Iron contaminants from the steel lids also can cause brown streaks in glass bottles, especially the clear ones.