The two year Colourite project attempts to help the industry absorb more green glass in its current production and was carried out for the organisation by Glass Technology Services in close co-operation with container glass manufacturers.
It explored the technical and aesthetic barriers to increasing cullet recovered from mixed collections that can be used in the production of new clear glass containers.
The project objective was not to counteract the growing level of mixed colour collected glass, but to highlight the affects that higher levels of mixed colour collections will have on clear glass colour quality in the future.
WRAP glass technology manager Andy Dawe said: In simple terms, the UK container industry has a large unsatisfied demand for clear cullet but an oversupply of green cullet.
This imbalance is being exacerbated by the growing trend towards mixed colour collections which results in higher levels of colour contamination and the additional loss of clear cullet during the sorting process.
In commissioning the project, we took a pragmatic view that these issues are here to stay and the aim of the project was to find ways to maximise the amount of cullet that container manufacturers can use in their furnaces from these sources.
Some significant findings and developments were:
-an acceptable quality can be achieved cost effectively by adding commercially available decolourisers to the furnace
-a robust but simple sampling method was developed to measure colour contamination with a user-friendly model to predict the effects of adding the decolourisers to already complex batch recipes. The Excel-based programme is already being used in the industry
-the development of a specification for colour contamination of processed glass which makes use of the new sampling method and has been agreed by both the glass processors and the container manufacturers
-in many cases the colour and clarity criteria adopted by glass manufacturers, brand owners and marketers are much more stringent than those required by the consumer
The full report is available at www.wrap.org.uk.