Tortillons come in all shapes and sizes like--but not limited to--the ones in the picture below (I pointed to the kinds I own. I also have some of those sand-paper pads that are shown--another helpful tool)
Everyone has their own teqniques, and here is my teqnique for how I use tortillions.
A little on the obvious side; the pointy tortillons are for shading small or narrow spaces (e.g. shading on the face under the lip, on the cheek, in the corner of the eye), and the fat tortillons are for blending larger amounts of graphite and have a small tip so you can get into some tight spaces. When blending an extra large area, I like to use a soft kleenex or cloth wrapped around my finger. You can also turn the pointy ones on their sides so this--red in above picture--is flat on the paper for smudging, but it leaves you with a smaller handle which is risky if you want to keep your hands clean. Ahem, which you do!
Hands work very well as smudging tools, but if your hands get too dirty, they can smudge parts of your picture by accident. Also, as you blend the graphite, it makes it easier to come off the paper, so you definitely do not want to touch it then. This is tricky for me because I like to rest my hand on my page for better control.
After using your tortillons awhile, they get pretty dirty. This is very helpful when you don't want to put much graphite down on a spot that only needs a very light touch of shading, so if the tool already has graphite on it, that is way easier than trying to put down a light amount by pencil, then blend.
Do you mean a smooth transitioning from light to dark? Or maybe you mean you can see your pencil strokes through your blending? If the pencil strokes are laid down too hard, and without uniform, they can sometimes be faintly seen through the smudging. This can be avoided by using softer pencils. A pencil of some kind is ideal because they have a softer core, which makes them blend nicely. 'H' pencils, 'F' pencils and mechanical can work too, but you can't press hard. Here is a chart of pencil grades:
To get that nice dark-to-light shading, you lay the shading down by pencil, dark to light (don't worry much about transitioning in this stage), then do the blending with the tortillon (now you can worry). With practice, the blending should bring out a smooth transition.
It is tricky to erase blended shading (like if there was a section that was too dark, so it was erased and patched) without it looking blotchy. If you need to erase, lightly tapping the eraser repeatedly to the page is a good method.
It is possible for a tortillion to get too much graphite on its tip, making it impossible to shade lightly with it. When this happens, wipe the tool several times gently in a soft rag or kleenex to get excess graphite off.
Small circles work well to blend, but short strokes work well too, depending on what effect you want to acheive.
There are plenty of tips and tricks to bring cool effects into your picture using a blending tool. I don't know all of them, just a few, and it is difficult for me to explain them without an example.
I reccomend this website:
Where I found several helpful lessons on drawing (including how to draw cats by anatomy), shading and using different tools. A word of caution, there are people who like to draw really weird stuff, and have posted how-tos for them .
The link I gave is the direct address to how to draw fire. I reffered to it when I drew the portraits for Riley, Xonos, and Emily with their flame-canes.
Btw, tortillons don't blend colored pencil very well, and I don't believe they are meant to. Besides, unless you wanted to mix the colors, you would have to designate a tortillon for each individual color.
Brushing eraser droppings or bits of graphite off the page with your hand puts your art at risk of being smudged (even just slightly smudged to where is is practically inperceivable until you apply an eraser to it) so brushing quickly and lightly with a cloth instead is advised. Blowing is also a great method, just be careful not to spit! (As I have done many times.)
This post is pretty long , I hope it is helpful and sparks some inspirations.
Have fun with your tortillions!