There are many details to consider when photographing an artists flat work. Whether it is on canvas or cardboard the type of materials an artist uses to complete the piece will present it's own set of unique variables. There is no way to anticipate the adjustments needed to obtain an accurate reproduction. This is why I do not recommend returning the original artwork until all the image details have been matched.
Each ink or paint etc. utilizes different pigments and all reflect light differently. The thickness, position, contour and media will alter the appearance further. When the artists mixes materials to produce a hue more to their liking, that reflected light is now even more complex. In short order, some of the colors perceived by the camera due to the pigments and lighting may be completely different than what the eye perceives. Insure you have compared and balanced your digital color file against the original in a natural light before considering the job done.
