Ivanko, York and Hampton have made all made aluminum plates. These are used for trade shows, studio shots, and as props for fitness shops and such. These are the best looking and weigh about 1/4 of a comparable iron disk.
Another common scam is the use of bumper plates, especially the black training bumpers or the old black rimmed Yorks. Depending on the brand, you can get up to 10lbs plates that are about the same size as a 45lb one.
If you ever get to see old episodes of the old HBO football comedy "1st and Ten", they used the bumper plate trick quite a bit.

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