Alrighty! As a whole you've done a good job here, but there are a few things that stand out that I can call out in order to help you continue to move in the right direction. That said, I'm really pleased with the observational skills you've demonstrated here, and the general attention to detail. You are also in a lot of ways demonstrating a strong grasp of how each of the individual textural forms sit in space, and how they relate to their surroundings.

What I'm going to touch on in my critique will focus on three primary concerns:

  • Textures with holes, or other kinds of areas that are prone to just getting "filled in"

  • The black bar on the left side of your gradient

  • Cases where the gradient itself isn't actually a smooth transition

To the first point, textures with holes, we can look at cases like the "sponge". What you've drawn isn't specifically incorrect, but it does imply that each of those sponge holes are infinitely deep, with no internal walls to catch any light whatsoever. For the sponge however, those holes aren't actually all that deep.

Instead of writing a lengthy explanation, I instead put together this diagram for you. Note how we have to consider the physical forms at play - not just the circle forming the hole at the top, but also the walls and floor of the hole, because all of these can catch light. Furthermore, if you look at the "correct" example, you'll note that we can actually create a gradient based on where the holes are relative to the light. If we've got the light source on the right side of our texture, and steadily everything towards the left is getting farther away from it, then naturally those cast shadows will get larger.

Ultimately holes can be tricky for students because it's not about the vacant space - it's about the walls and floor that surround it.

The next point is the black bar on the left side of your gradient, and it's relatively simple to explain. In the instructions for the texture analysis exercise, students are told that this black bar serves a specific purpose - it is meant to blend seamlessly and smoothly into the gradient, with no clear distinction between where that bar ends, and where the actual texture begins. Through most of these, you didn't quite achieve that obfuscation of its edge, and in some cases it's extremely noticeable, like the broken glass (which admittedly was a tricky one - I'd have gone more with broken pottery or something, just so you don't have to needlessly deal with transparent materials) - as well as the turtle/tortoise skin. Conversely, your loom weave texture is much better in this regard.

What we want to demonstrate here is a clear, smooth transition from light to dark - no big jumps. We achieve that not by working with lines and outlines, but rather by ensuring that every mark is itself a cast shadow shape, and therefore freely able to get larger or smaller based on each textural form's relationship with the light source. Changing the shadows when working implicitly like this does not change the nature of the forms being conveyed. As shown in this example of bush viper scales, using more or less ink does not change how many scales are present and how they're arranged.

Lastly, I want to look at a specific instance where your gradient isn't that smooth of a transition. While these others have had the sudden jump from that black bar into the texture proper, the texture has generally had a fairly smooth transition the rest of the way. Your leaf texture however, suddenly ends up with a big heavy shadow from that central vein.

Keep in mind that the goal for this gradient is not to take the entire texture and just arrange it as a gradient - rather, the texture is a source of information. How those textural forms are arranged is subject to that information, but the choices you make are ultimately your own. In general, for something like this I wouldn't necessarily work with really different textural forms (that central vein is a lot bigger than the rest, and thus will inevitably given the same lighting scenario, cast a heavier shadow). I would instead keep my textural forms more consistent, choosing to pick from a tighter area of my source leaf where it's pretty much all just tiny veins. This is by and large how your other textures have been done.

That about covers it. While there certainly are things for you to keep in mind here, by and large you've demonstrated excellent observational skills, and I think your grasp of these spatial relationships at such small scales is progressing well. Just be sure to keep at it, and I would recommend looking at the "hole" diagram every now and then, letting it sink in more and more.

I'll go ahead and mark this challenge as complete.