There are two main types of contamination in glass: material contamination and colour.

Contamination

Three levels of contaminants are stated as below:

1. Unacceptable contaminants
   Any medical or chemical refuse, needles and syringes; bottles and jars containing any liquid or solid hazardous or toxic material, coal or coal dust.
2. Critical contaminants
   Ceramics such as crockery or earthenware, Pyrex cookware, Visionware glass saucepans, inorganic materials such as bricks, concrete, gravel, stones etc and non-container glass such as flat glass, laboratory ware, light bulbs and tubes.
3. Hazards
   All non-magnetic metals, particularly aluminium and lead. Wire, strapping, wood, plastics, textiles and materials.

Colour

There are three main colours of glass: clear, also known as white or flint; green; and, brown, also known as amber. Different glass collectors specify different degrees of colour separation in container glass.

In recent years some companies have developed high-tech colour sorting equipment in order to combat contamination by other colours. Some collectors will also take mixed glass as well as colour-separated.

Cullet

In 2006, the Waste & Resources Action Programme published a standard, known as PAS 101, which gives a specification for recovered glass and outlines grades that can be applied to tipped loads.

PAS 101 seeks to harmonise various independent specifications to provide a comprehensive specification for all raw container glass collected in the UK for recycling. It introduces a four tier grading system for raw cullet quality - grades A to D - according to the degree of colour separation, contamination and particle size.

Grade A

Cullet type	White flint (clear)	Amber (brown)	Green
Permitted contaminant	Other colours 4%	Other colours 5%	Other colours 5%
Contamination: No more than 0.5% organic, 0.1% ferrous and 0.2% non-ferrous.

Grade B

Cullet type	White flint (clear)	Amber (brown)	Green
Permitted contaminant	Amber (brown) 6%	Other colours 15%	Other colours 30%
Contamination: No more than 0.5% organic, 0.1% ferrous and 0.2% non-ferrous.

Grade C

Cullet type	White flint (clear)	Amber (brown)	Green
Permitted contaminant	Amber (brown) >6%	Other colours >15%	Other colours >30%
Contamination: Up to 1.0% organic, 0.2% ferrous and 0.4% non-ferrous.

Grade D

Cullet type	White flint (clear)	Amber (brown)	Green
Permitted contaminant	Amber (brown) >6%	Other colours >15%	Other colours >30%
Contamination: Up to 3% organic, inorganic, ferrous and non-ferrous.

One independent company’s specifications are set below:

Berryman's specifications

Cullet should consist of container glass only. Glass should not be deliberately crushed and bottles should be kept as whole as possible. If a load has contamination levels greater than in the guidelines below, it may be reclassified as mixed for use in alternative markets.

Maximum degree of cross-colour contamination permissible in colour separated glass

Cullet type	White flint (clear)	Amber (brown)	Green
Permitted contaminant	Amber (brown) 2%, green 2%	Other colours 20%	Other colours 20% (exc blue)

Quality Protocol for Flat Glass

WRAP published a Quality Protocol for flat glass in January 2009. The Quality Protocol sets out criteria for when the material is no longer classed as waste and is intended to increase customer confidence in the material.