I have been interested for quite some time in creating large cyanotype prints, so far I have been able to get up 34x28 inches, below is an example. I used a rod and brush to coat. I really would not want to go any larger, although i have a reasonably large darkroom the developing trays required for any larger would make life quite difficult. I recently came across the work of Christian Marclay whose cyanotypes are around 100" wide (over 2 and a half meters long) which must be challenging. Thank you 'Worker 11811' for the link regarding inkodye, have reblogged about it.