Thinking about packaging specifically*, where the plastic colour doesn't necessarily have to have a decorative/aesthetic function (or need to be e.g. clear/tinted to function; sunglasses etc), would it not be helpful to recycling goals for the government to just mandate that plastics for packaging can be one of eg 9 (rainbow 7 plus black and white) different types of plastic (PET, HDPE, LDPE, PP, PS, PVC etc) and each variety has a defined colour to aid identification for recycling

I know they're supposed to/increasingly have a recy-triangle with a number in, but it's hard to read on some packaging, and what if you only have a fragment that doesnt have the triangle on? Surely being able to say "it's a food container and it's yellow. It's HDPE" would be better, even if it meant everything in the fridge was suddenly in a blue container etc; manufacturers can use the sticky backed paper labelling to make their product stand out..

* but I'd extend it to everything

Those plastics look similar in visible light, but they naturally have different 'colours' under infrared light (they reflect different IR wavelengths). The machines used to sort recycling, use high speed IR cameras to identify the material of each bottle that comes down the conveyor, and divert it into the correct bin.

Some more ideas here

https://www.chemistryworld.com/features/the-plastic-sorting-challenge/4011434.article#/

Edit to add: it's good to avoid products in black-tinted plastic packaging, meat trays etc, as the machine can't see the IR colour through the black pigment. And to peel off those plastic film lids from trays and film bottle labels as they confuse the machine.

INteresting article Will; it pointed out that, in a sense, the notion of "colour me different" is coming in - it's jsut that the coloration is in the UV spectrum rather than the visible light. Good to know!

It's a nice idea and would make recycling so much easier. . It seems to be sorting the stuff that makes recycling so hard and therefore costly so I wonder why there has to be so many different types of plastic in the first place. Can't we just have one type and then there would be no sorting conundrum and all plastic could be recycled. If certain jobs that plastic performs aren't achievable with the one type that my, admittedly, idealised scenario would allow, use something else for that job.u