printing black on large areas of canvas

[RafalWM]

earlier today I picked up a canvas print I had done for one of my clients in a local large format printing shop (solvent). The colors turned out nice, but the large areas of black are much too light. It looks like around 70-80%. I'm guessing the material absorbes a lot of the ink because they said they did the maximum possible.
The two questions I have are:
1) could they have applied something onto the canvas before printing, so it wouldn't absorb all that toner?
2) can I apply something on the material now to make the image darker and colors more saturated?
the print size is around 6x4 feet.