 An earthship is a perfect example where different re-use models are used, including cradle-to-cradle design and permaculture.A major constraint in the optimal recycling of materials is that at civic amenity sites, products are not disassembled by hand and have each individual part sorted into a bin, but instead have the entire product sorted into a certain bin.This makes the extraction of rare earth elements and other materials uneconomical (at recycling sites, products typically get crushed after which the materials are extracted by means of magnets, chemicals, special sorting methods, ...) and thus optimal recycling of, for example metals is impossible (an optimal recycling method for metals would require to sort all similar alloys together rather than mixing plain iron with alloys).