Q. What does a "wood conditioner" do?
A. Certain woods have areas of varying density. These areas absorb stains at different rates, creating darker spots, known as blotches. A wood conditioner simply soaks into the wood, with the more porous areas absorbing more conditioner. This controls the absorption of the colored stain, lessening the differences between the more and less porous areas of wood. This makes for less blotching.
Substances that I've successfully used as wood conditioner: Branded Wood Conditioners (Minwax, Ben Moore, etc...) Mineral spirits or turpentine "Natural" stain of the same brand in use A thin shellac (1/2-1 lb cut) spit coat Thinned varnishes Oils, such as thinned boiled linseed oil
In short, any substance that soaks in and is compatible with the stain will work. Some of the substances soak in faster than others, some need to dry before the colored stain is applied. Practice on scrap.
Barry