I engraved a design on a clean, heavy, cotton Tee shirt.  It looked perfect and I was very pleased.  The shirt is a medium brown, and the processing left a nice light gray color.  At this point, there was no ash or dust apparent, and nothing to brush off.  When I washed it after wearing it once, the image disappeared.  Only a very faint dark shadow, and some damaged threads were left.  Where should I start to figure out what went wrong? 

M1 at 32% and 250mm/s, 1 pass