Upon first seeing this shiny fabric background, you might think "Gradient Mesh." And if Gradient Mesh intimidates you, you might just click to the next tutorial. In fact, achieving a rich, satin background is deceptively easy. Illustrator's Blends are the key. Let's get started!
Choose a color scheme. You'll only need four colors, which have an equidistant range of values. That is, a highlight, a shadow, and two shades in between. The Color Guide panel can be useful when choosing colors. Click the pull-down menu to reveal various sets, all based on color theory. Or just use the values below. Once you have the four colors, click New Color Group at the bottom of the Swatches panel to store your swatches in a neat group.
Note: For the rest of this tutorial, I will refer to the colors numerically, with the lightest being 1, and the darkest, 4.
Start at the top left of the artboard and draw a triangle, using the Pen tool (P). It can extend beyond the left and top artboard edges (we'll clean it up later). Fill the triangle with color 2. Now draw an ellipse with the Ellipse tool (L), positioned at the left edge of the triangle.
Select both objects and go to Object > Blend > Make. Your blend should look like the image below. If it looks choppy, undo, then double-click the Blend tool. Choose Smooth Color as the spacing method and try again.
Draw a thin rectangular shape that aligns with the bottom of the blend. Fill it with color 2. Then draw a smaller shape inside this one and fill it with color 1. As before, make a blend. If necessary, adjust individual points of the blend objects using the Direct Selection tool (A), so it looks like a cylinder, with a highlight on top. The blend will update as you move the points.
Carefully position this second blend alongside the first one so that no white shows through. Again, you may have to adjust individual anchor points.
Make another blend, this time with a larger, curved quasi-triangle as the base, and an amorphous ellipse for the highlight. You can draw the highlight shape with the Pencil tool (N). Hold down the Option (PC: Alt.) key at the end of the stroke to close the path.
At this point, it may be hard to visualize the end result, because of the ragged edges. You'll use a Clipping Mask in the last step to tidy it up, but for now, you can make a temporary frame around the artboard to hide them. First draw a square the size of your artboard. Then go to Object > Path > Offset Path. Enter a value large enough to cover the rough edges and click OK. Now select both squares and go to Object > Compound Path > Make. Fill with white, and put this frame on a new layer above the blends layer. Lock the frame layer. Now you can continue working on the bottom layer, without seeing the edges.
Draw a large shape whose top edge closely matches the bottom of the previous blend, and then extends about two-thirds down the artboard. Fill it with color 3. Offset the path by about -20 pixels, and fill the new path with color 2. Now draw a free-form shape with the Pencil tool as in the image below. Fill it with color 1. Select all three shapes and blend them. Send this object behind everything else, and adjust if necessary, so that there are no gaps.
To add depth and realism to the image, you can create more blends and place them on top of other blends. For example, make a three-step blend from some freehand ellipses. Carefully place it (and subsequent blends) on top of the large blend from Step 6. Make sure that no area of color overlaps an area of different color. In this example, the small blend is situated on top of a large swath of color 1. Since the small blend's bottom color is color 1, the result is a smooth transition. Sharp edges are undesirable.
Continue making blends until you reach the bottom of the artboard. Vary their size to add interest. For added depth, I created a corner fold which consists of one blend stacked on top of another. To achieve the highlight on the edge of the fold pay careful attention to how the two shapes interact. Adjust individual points with the Direct Selection tool (A). You can also use the Group Selection tool (white arrow with + sign) to select and move individual objects within a blend.
After all the blends are in place to your satisfaction, you may leave the white frame in place, or create a clipping mask. To do the latter, draw a rectangle over the area you want to show, then select both the blends and rectangle and go to Object > Clipping Mask > Make. Your final image should look something like the image below.
With Illustrator, there is always more than one way to achieve a desired look. Each way has its advantages, but often it's a matter of what you're used to and comfortable with. Some people might find Blends easier and more flexible than Gradient Mesh. Once you perfect your blend-making technique, you'll find that the blends are the easy part. The success of the final result lies in the careful positioning of each blend, and the relationship between each. Once you've mastered this technique you can create a variety of flowing fabric backgrounds.