How to Avoid Seeing the canvas through your work
I have just started needlepointing and I'm making a belt. For the most part, my canvas is covered....but I still can see some of the paint, from the design on my canvas, through the stitches.
Am I pulling the thread too tight? Or not using enough yarn (I'm using wool)
For the blocks of color I have been using basket weave, and I can still see some of the canvas even in this stitch.
What am I doing wrong?
You do not mention what count your canvas is (how many canvas threads per inch), but it sounds like you may not be using a yarn that is thick enough.
The yarn should not be so thick that it pulls the canvas out of shape, nor should it be too thin, otherwise you will be able to see the canvas threads between the stitches.
To an extent is also depends on the type of stitches you are using for your project.
For diagonal stitches, such as basketweave, you can get away with a thinner thread, but for vertical or horizontal stitches a thicker yarn, or more strands of something thinner, will be needed in order to cover the canvas sufficiently.
For crossed stitches, or where a second "layer" is stitched on top of other stitches, you can also get away with a thinner yarn.
Tapestry wool is generally used on 10 - 14 count canvases. For higher counts you would normally use stranded yarns, such as persian or crewel wool, so that you can vary the number of strands as required for the stitches utilized in the design.
If you are working a kit, where the yarn was provided for you, and are finding the canvas threads show through your stitches then it could certainly be a tension issue. Many needlepoint beginners tend to pull their stitches too tight. It takes a little practice to get the tension just right. You want them to just lay comfortably on the canvas, with no distortion of the canvas threads. On the other hand you don't want to work so loosely that the stitches can get easily snagged.
I hope this has helped.