Re: Strength of Different Woods for Book Shelves
The wood species that have been mention; pine,fir,poplar or even birch, are all considered soft woods when it comes to staining. To avoid a spotchy look, they require a pre-stain conditioner. A conditioner is merely the clear liquid which the stain is made from. It is applied liberally, allowed to soak in for a couple minutes and then completely wiped off. The theory is that those soft, porous portions of the wood will absorb the oil and the harder portions will not. When wiped clean, the boards will have similar porosity so that when the pigmented stain is applied, it will go on evenly. The stain should be applied within two hours of the pre-stain.
After allowing the stain to dry for at least several hours in a warm room, your finish may be applied. If using a urethane varnish, at least two coats are neccessary. A third coat gives better protection.
Many woodworkers dislike urethanes, feeling they give a somewhat plastic appearance. On a light traffic cabinet such as a bookcase, you might just use a couple coats of danish oil as your finish on top of your stained wood. Danish oil gives a nice patina and does not scratch in the same way as a brittle urethane. Danish oil is very easy to apply, just wipe on, wait a few minutes and wipe off what has not soaked into the wood.
If however, wet items are ever to be set on it, stay with the more durable urethane.