It may help you target your adjustments if you shoot with a known target in a reference shot. I made up an example on copy paper (with OBAs, so paper white is bluish) and some various hardness pencils. I shot with a CCPassport and targeted my black, mid and white levels based on a black of ~L20, mid of ~L50 and a white of ~L96. See screenshot. I shot with natural window light and exposed so that the raw file was just below clipping - I used the raw histogram in the Magic Lantern firmware for my 5DIII to set the exposure. Confirmed this with Raw Digger.
I used ACR 9.1 in PS, PV2012 for this example - the automatic highlight compression process version - and the same controls, etc. apply in LR. I assumed you are using PV2012. This example used the AdobeStandard camera profile with all other ACR settings factory defaults, linear tone curve. I click-white-balanced on the neutral WB patch in the lower half of the CC Passport in the image (the ones with the dimple under them).
The Exposure control moves the midtones around, so I used it to target the mid gray in raw conversion to bring the mid gray patch down to ~L50. I used the white and black controls to stretch the histogram to the approximate points on the black and white ends of the CCPassport patches - the Contrast control permits you to scale these adjustments inward or outward from the center of the histogram. Finally, once you get things generally lined up with the CCPassport patch values, you can decompress the highlights using the Highlights slider. This will restore contrast to the highlights. You can do the same with the shadows using the Shadows slider.
Once I made the conversion into PS, I made a slight curves adjustment to the highlight end to remove the blue cast from the paper white (the OBA effect). I also added some local contrast to the low contrast content of the scene (the very light tones next to paper white) with Topaz Clarity, low contrast boost. The artist may or may not desire these kinds of changes, but they may add to the photographic representation of the work.
If you shoot under controlled lighting, this may work as a preset after you have experimented with enough similar pieces, paper types and media. The amount of stretch you apply to the histogram may be used to to blow out or preserve paper white and paper texture, and tweaks to the individual color channels to set the paper color (in the highlights) can be made as well. Because these are Curves operations, you can do them in LR. I tend to think in terms of LAB color, even if I am working in RGB, so I set up my conversion space in ACR to be LAB so I could get the LAB histogram and color sampler readouts. The direction of the lighting and the contrast control during image acquisition between paper texture and medium (like ink or charcoal or pastel) can probably be modulated somewhat by the directional aspect of the lighting, if that is an issue or you want to emphasize one aspect more or less for a particular piece. I shot with uncontrolled window light for this example, so it is by no means a controlled process with uniform, well-characterized lighting.
Just another approach, maybe it might be more intuitive or a viable alternative to the LR Tone Curve that some mentioned might not have enough precision. Any way you do it, shooting with a known reference target is very helpful - you can target and alter the highlight and shadow compression against known values instead of trying to eyeball it. Because the dynamic range of the subject is not very wide, you can uncompress the highlights and shadows with the sliders to re-establish contrast in the subject, once you establish the midtone and black and white points.
Kirk
Image 1 - ACR settings
Image 2 - After raw conversion
Image 3 - With PS tweaks to highlight color and low contrast boost
