When you work on master copies, you should have a set of goals of what you’d like to learn from the exercise. For example:
-To emulate how a master handles brushwork
-To understand how a master uses color
-To learn how a master manages values
-To learn how a master depicts forms
-To learn how a master handles anatomy/figure, backgrounds, etc
And so on.
Doing copies and doing studies are two different things. A copy is an exact copy (as close as you can possibly get, almost like an art forger who’s trying to create a fake version that looks indistinguishable from the original–or along that line of mentality). A study is a lot less refined and done only to the level of polish needed to learn specific lessons. For example, if you wanted to study how the master handled composition by using contrasting values, colors, shapes, spatial arrangement, etc, then you don’t need to do a detailed copy to learn that–a simplified study will be enough.
In your case, you want to do a value study, so as long as the values are more or less intact (without needing the micro-details and refined rendering), it’ll work just fine. What you want to learn from the process, is how the master manages his values so all the forms are clearly readable without confusion, all the main shapes in the composition are well separated and creates an effective tonal composition, how contrast is pushed or flattened to create focal points as well as convey spatial relationships.
I think you did a pretty good job with your value study. The forms all read clearly and the overall values/contrast is conveyed fairly accurately. There are a few spots that aren’t quite right, such as the spot between her breasts being a bit too light in value, and the background not reading as clearly as it should (you are not assessing the background elements as logically as you should and asking yourself what you’re actually depicting, and are just copying the values/shapes, which leads to a jumble of shapes and values that don’t read clearly as actual forms of tangible objects).
Some people convert the colored reference into B/W first so they can just totally focus on the values and not be distracted by the colors. Some people are fine with constantly squinting when looking at the colored reference to reduce the influence of colors and assess the values. You seem to be doing fine without having to convert the reference to B/W.
And yes, master copies/studies are extremely helpful and has always been a time-honored aspect of academic training for artists. As long as you keep in mind the lessons you’re supposed to be learning as you do them, as opposed to just doing them mindlessly without any critical thinking.
Once you are comfortable doing these (including doing studies of photos), you can start to challenge yourself more by working from life, such as doing still life, portraits, figures, landscape, etc. And if stylized artworks are also of interest (such as comic books and animation), studying stylized artworks and understanding how they relate to real-life counterparts will also be very important (analyzing exactly what the artists simplified, exaggerated, or idealized in their stylized versions).
