Never tried this, just a thought - what if a coat of spar varnish (UV resistant marine polyurethane) were to be brushed over the written-upon label? Of course that would negate potential reuse, but for a venetian blind slat cut into label, who cares about re-use. Judy in somewhat sunny but chilly New Jersey where Galanthus 'Potter's Prelude' is in bloom in the open garden