When using a NGR stain do you try to pick a color that is close to, but not as dark, as your final color?
From contributor K:
Rule number one of staining: do finished samples first! With NGR's and other dye stains, it is always possible to thin them to a lighter shade or to add other dye colors. If a dye stain is applied fully wet, it will give you an idea of what the color will be once a finish is applied. Typically, once a dye dries on the wood, the color will have a different look that it will after a finish is applied. If for some reason, you decide that the color is too dark after you have applied the dye, you can wash it out by wiping it with the appropriate thinner, but that can produce an uneven effect and can be time-consuming. Itís better to develop the color that you want by using sample boards, then applying the dye to the piece.
Keep in mind that once a dye is flooded on and allowed to soak into the wood and dry, applying the dye again will not darken the color. That is not true if you are adding the NGR to your finish. As you apply each coat, the color will get darker. Also it takes more finesse to apply the color evenly.
So that is one way that you can use NGRs - alter the base color of the wood to set the tone for the stain. For example, I know a lot of people start out staining walnut with a yellow NGR to help warm up the base color.
You can also just take an NGR that kind of matches your stain color, and use it to darken the wood initially, then go over with the wiping stain. Not only does this create a very rich and deep looking color, but it also helps to eliminate blotching on woods such as maple, cherry, birch, etc.
So how do you know what color NGR to use - samples and experience. Spray up a bunch of pieces with various colors of NGR's, seal with a washcoat, then start putting different color stains on them to see how they affect the final color. You should have samples with just the wiping stain to compare to a base reference so you know how the NGR has affected the final color. As contributor K points out, make sure you put a clear over top of your samples as this will drastically change the color of the dye/stain.
After the NGR has dried, I will apply a 5% washcoat on top of the NGR. To make a 5% washcoat, you first need to find out the solids by volume of your clear coat, and then thin it till you get to 5% solids. Spray a normal wet coat with the washcoat.
After the washcoat has dried, rub a fine ScotchBrite pad over the surface to just help smooth out any grain raising, etc. Just a quick swipe with the ScotchBrite is all that is needed. The washcoat is used to help prevent the NGR from lifting when you apply your wiping stain and also controls blotching of the wiping stain.
Next apply your wiping stain as you normally would. Spray or wipe on, then wipe off. When the stain is dry spray a clear coat. Sand this with a 320 grit sponge and then spray another coat of clear and you are done. If the color needs to be altered, I will add a toner coat between the two coats of clear.
Knowledge of the properties of stains and finishes is all-important. For instance, oil-based stains are not designed to be used over a finish coat. And that can pertain to a wash coat applied too heavily. The finish may have filled the pores of the wood, so the less there is the less area for the pigment to reside in. Since there is very little bit" of the stain into the finish, it mostly gets wiped off. Having said the above, have I ever used an oil-based stain over a finish coat? Yes, but it has to be applied extremely light and it has to fully cure over a few days before I can apply a finish. That's just one technique and it is not for everyone.
I say all the above to point out that there are hundreds of possible ways to apply color and finish to wood. I know that you are looking for specific answers, but the last place to experiment is on the customers' pieces. You have to find the processes that consistently work for you. We on the forum may tell you what to do, but until you see the results, using your own eyes and taking into account your own particular spraying capabilities, it won't mean much.
The key is to learn what colors of dyes and/or stains (or their combinations) plus the techniques will produce the desired (hoped for) end result. The other key is to be able to produce that result again and again. There are many books on the market about finishing. Woodcraft keeps them in their stores. If you can, go look them over. The best books show color photos of the processes. Buy two or more different books.
Off of your topic, but contributor F's statement about warming up walnut is true. When filling walnut I use an orange-colored filler. Most of us might think that putting orange in would be garish, but it produces a stunning result and there is no evidence of a strong orange color visible.
It is a money-loser to try to experiment with a new technique or process on a customer's piece. One of the important aspects of a successful shop is reproducibility. To the degree that you can, set up a series of sample cabinets using the woods that you typically use, or at least doors that your customers can review and choose from. Really it will simplify so much. Now the customer has something concrete to choose from. That is better than describing sort of a medium dark brown to a customer, because it will be a given that the color he sees in his mind's eye will be different than what you are picturing. The customer saying, "door #3" takes out the guesswork. The truth of the matter is that you can make the finest cabinets in the world as far as the construction quality goes. If the color and finishing isn't done correctly in the customerís opinion then you will not prosper.