As a whole, you've handled this challenge quite well, with two main points standing out as points to discuss. One of these points is a more consistent issue across the set, while the other is something that comes up here and there, and could also be a misinterpretation on my part of what you've drawn, but discussing it should still be valuable.

Starting with the first issue, it has to do with the hard black bar we place on the far left of our gradients. This bar, as noted in the second paragraph of this section (along with the white bar on the opposite side) serves to create the extremes between which we use our texture to create a seamless transition from black to white. The key word here being seamless - there should be no discernible hard edge to the black bar, but rather we should not be able to determine the specific point at which it ends and the texture begins.

In order to achieve this, we have to rely quite heavily on the shadows being cast by our textural forms. In this exercise, we draw our texture from a top-down point of view, looking straight down on the surface upon which the texture is applied. If seen from the side however, we'd see something a little more like this, with the light source on the far right, and the textural forms standing in various positions.

When the textural forms are closer to the light source, the light rays hit it at a steeper angle, resulting in a short shadow. When the textural forms are further away, the light ray's angle is much shallower, resulting in a longer shadow. So, through this arrangement, our gradients are naturally predisposed to have much more black, with much larger shadow shapes, the further to the left we move (away from the light source).

It doesn't actually matter how many forms there are, or how densely packed they may be - we can continue to swell these cast shadows larger and larger, in order to break up that straight edge to the black bar, and integrate it more seamlessly into the overall gradient.

Keep this in mind when working on this exercise in your own practice in the future - the bar is not something to be drawn and then ignored, it serves a purpose that influences the manner in which we think about our textural forms and the shadows they cast.

Now the second point I wanted to make is basically that while in a lot of places you make excellent use of the shadows cast by your textural forms (I'm especially pleased with number 25 which focuses on the shadows being cast by the threads themselves), there are some spots where it seems that you may be using your filled areas of black to capture form shading rather than cast shadows. This is an area where students can often get confused, because in the end result they can look very similar, but they are very distinct. The biggest distinction between them is that cast shadows have the advantages of being implicit marks, while form shading is still very much explicit.

Where drawing a cast shadow requires us to first design a new shape, the very design of which captures the specific relationship between the form casting it and the surface receiving it, if instead of designing a new shape we find ourselves simply filling in a shape that already exists as part of the construction, this is more likely to be form shading instead, where we're actively making a surface that points towards the light source lighter, and a surface that points away from the surface darker. So if you catch yourself filling in a shape that is already present in your drawing, then take a step back and ask yourself if you're really adding a new shadow shape, or not.

The difference is that if we use explicit markmaking like form shading, we're forced to still draw and construct every single textural form - the shape of a given side or plane of the structure already exists, and so there's no modifying it - it simply gets filled in as it is. Conversely, when working with cast shadows, we have much more control to dictate whether we want a shadow to be large or small, based on the situation at hand.

Now again - I'm not actually sure if you did have instances where you were shifting more towards form shading. Cases like 4 and 5 were harder to determine, along with some other cases. Long story short, there was enough uncertainty that I figured it was worth offering the explanation.

Anyway, all in all you've got plenty of cases where y ou're clearly working with cast shadows, and using them quite effectively, so you're definitely headed quite confidently in the right direction. Just be sure to keep these points in mind.

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