I did this little zendala last night and tried out a new pencil for shading it. I had recently purchased a new pack of the Derwent Shading pencils and wanted to put them through their paces. I was pleased with the results with only a few minor quibbles.
I tried out all the pencils in the pack. First I drew a right angle with my pen so it would be similar to what I do when shading a zentangle. For each pencil I drew two squares - one using very light pressure and one using heavy pressure. Then I used a paper stump (tortillian) to blend the mark out. I also used my two types of Zentangle pencils so I would have something to compare them to. Also in the pack of pencils I found a 8B sketching pencil that is water soluble. This gave me more ways to play with it.
I found they all worked pretty well. My favorite however was the Derwent HB pencil. I liked the intense dark I could get but I also found it blended the best. The water soluble pencil 8B Dark wash also gave me some neat results that I'll be playing more with later. Some of the pencils were harder to blend - especially when I used heavy pressure. That will be correctable by simply applying less pressure as I do the shading. The other minor quibble I had was that the Derwent pencils are too thick to go into my electric pencil sharpener. Again, easily fixed by pulling out my hand held sharpener designed for thicker pencils.