gmcIf you can guess what this is, you have my awe!
It's print paper for sure, but it's not thermal. Instead, it's for 'spark printing'. The silvery coating is conductive, and the printer would zap current through the layer to burn away the coating revealing the underlying black background.
It's for use in the Sinclair ZX printer (compatible with ZX-81 and ZX Spectrum).
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