Like cornices, the selection of valance styles available gives you many options to enhance your window treatments. You can choose from a plain straight shape, or vary the base. You can add trims and contrast edgings, or keep things simple.
Here are some more details.
This is the most widely used shape you'll find for valance styles. It lends itself to all window sizes, and is the easiest to make.
The most important part of a valance is the heading. By using different styles, depth and accessories, the heading defines the whole character of the finished look.
The heading depth for your valance can be deeper than you'd normally use for a curtain. I'd suggest you make the heading at least 3" (7.5cms) deep, and preferably more.
The wider the valance, the more important it is to make sure the heading is the correct depth.
If your valance is quite deep, you may need to make your heading deeper to keep it in proportion. If the overall depth is 2'0', then you could make your heading 4" or even 5" deep instead of the usual 3". This is where making your headings by hand using buckram is useful, because you can make the heading measurement any size you want.
I've always found that shaped valances look best on tall windows.
Wide windows can take them as well, but you need to be very careful with the varying depth. To get any real effect the sides often have to be quite deep.
The depth should be about one fifth the drop of the curtains. For shapes, the center can be less, and the depth of the sides more.
If you're not sure, make a life-sized template from lining or paper, and attach it to the window in question.
Here's an important tip:
Shapes can take other forms as well. Scallops work well when you don't want a straight base, but sloping down at the sides isn't feasible.
What sort of fullness should you use for your valance styles? I suggest you use the same as for the curtains. Don't forget to include the sizes of the returns when you work out the total width.
If you have included interlining in your curtains, then include it in the valance as well. If you don't used interlining, it's often a good idea to put interlining into the heading to give it more body.
You can give a plain valance a lot more interest by adding accessories such as trimmings, fringes and so on.
Just one example, you could take some decorative rope and loop it between the pleats of a Goblet heading. Use a matching plain fabric to make a trim along the base.
If this is your first time, then I suggest you begin with a simple shape and heading. This will give you confidence when you start to attempt more advanced ideas.