Certain specific stain products are compatible with varnishes such as TotalBoat Lust or TotalBoat Gleam and can be used, but it is not the preferred method of adding a stain. There are no specific stains, or brands that are recommended to be used with TotalBoat Lust or Gleam.
Compatibility is possibly the most important factor. Most stains will say whether they are designed for being mixed in with another product. Some stains are stand-alone products and should not be mixed into other products. Most stains are designed for either water-based products or oil-based products.
TotalBoat Lust and TotalBoat Gleam are oil based, therefore, any stains added to these products must be compatible with oil-based products. There are some specific brands such as Minwax® and some other hardware store-grade stains that work great in their own proprietary systems, but are known to have poor results when used with TotalBoat brand varnish products.
Stains are generally most effective when they are applied directly to the substrate, such as wood, in most cases, when used in collaboration with varnish. The stain will work its way into the grain, and accentuate the grain tonality of wood, and give it a new color. When a stain is added to a varnish, it is more convenient for application, but it is diluting the resin of the varnish, at the same time creating opacity. For exterior applications, this is not good for the varnish. The increased opacity will absorb more sunlight in the coating, leading to much faster degradation of the varnish.
It is always advised to test any stains before applying them to the final project. Always give the product ample time to cure, and observe the results to see if the stain is creating the desired look.