Background fluorescence. A series of pieces of linen placed one by one on a china plate in an oven for ten minutes, with the oven (and plate) having had time to warm up to the next temperature for ten minutes between each sample. Sample 1. Uncooked! Samples 2 – 8: 180C – 240C in 10C steps. After taking them back to the lab, they were all lightly brushed in one corner with a red hot spatula. The fluorescence due to the spatula iv visible on Samples 1 and 2, but pretty well masked by the rest.