Hi Stuart,
I have made PCBs with transparencies for many years.
20 years ago I made the transparencies with an HP color laser printer
with good results.
Then when replacing the old color laser printer with a new eco black/white
laser printer the black areas were not completely black anymore. I tried
several different laser printer with similar result.
I then tried an ink jet printer which had higher resolution. The critical part is the transparencies used.
I tried several different before
During the last years I have used a Canon IX6550 ink jet printer and transparencies from
Mega Electronics LTD in UK. It is JetStar Inkjet Premium Artwork Film, order no 100-075.
This film gives a very good quality transparencies which I use for smd/microwave PCBs