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It's always a good idea to test out your finishing method. But on a big project, I would argue that it should be considered to be mandatory.
I'm planning a project which will involve cherry plywood and solid cherry. I use cherry frequently, so I'm pretty sure of a good finishing method, but I still thought I would take the time to practice first.
I started by preparing a test piece. I cut a surplus piece off of the end of the project plywood. I prepared some solid cherry stock as well, and sanded both of them up to 220 grit. I then tacked the solid cherry to the plywood, dividing the plywood piece up into five sections.
This gives me five separate sections where I can test out the finish, and it includes both plywood and solid cherry as well.
I have three cans of finish that I am going to be testing in various combinations. First, I have Minwax oil-modified polyurethane. (I AM NOT SPONSORED BY MINWAX). I was introduced to this finish a few years ago and I like it a lot. It has the easy cleanup and low-VOC of waterbased finish. But it also gives a bit of the warm amber colour that you get from an oil-based finish.
I also have some pre-stain conditioner. This is intended to help prevent uneven absorption of stain. It is also supposed to help with blotching. As a side note, I've been using cherry for almost 20 years and I really have never been that bothered by supposed "blotching" in cherry. I just love Cherry and it's rich look.
Finally I have some dewaxed shellac. Shellac has a lot of uses. For one thing it can go over or under just about anything. It also adds some nice colour to cherry. On it's own, it does not provide much protection unless you pile on a LOT of coats.
In the first section, I applied two coats of the polyurethane.
In the second section, I applied one coat of Shellac, followed by two coats of polyurethane.
In the third section, I applied one coat of the pre-stain conditioner, followed by two coats of polyurethane.
In the fourth section, I applied one coat of the pre-stain conditioner, followed by one coat of shellac, followed by two coats of polyurethane.
And in the fifth section... I did nothing. I did not have any other methods to test. A Polyurethane topcoat was mandatory for these cabinets, so I was not testing any sort of oil finish, nor was I trying out lacquer. And shellac alone was not going to be strong enough.
When necessary, I lightly sanded with 220grit sandpaper between coats. I was not really concerned with the feel of the piece in this test, I was just trying to evaluate the look of the finish.
I applied two coats of oil-modified polyurethane using a foam brush. Normally I would apply 3-5 coats, depending on the use. However, those final coats only add more protection; they do not really affect the looks that much.
The final results were challenging to show in pictures or video, as the differences were subtle.
I found that the two sections treated with the pre-stain conditioner looked a bit more dull or flat compared to the other two. On their own, they looked fine, but when compared to the other two I could see a difference. So the pre-stain conditioner was set aside.
That left the section where I just applied two coats of the poly, and the section where I first applied some shellac, followed by two coats of the poly. Both of these sections looked very nice, with vibrant colours. However, I would have to give a slight edge to the section where I first applied the shellac.
However, the difference there was very subtle. I also have 15-20 years of experience with cherry, so I know that the appearance will change over time, becomeing darker and richer with time and exposure to UV light. So I think the "poly-only" section will likely "catch up" to the "poly+shellac" section pretty quickly. Therefore, for my purposes, I am selecting the simplest solution, which will be to just use the oil-modified polyurethane on my project.
Thanks for reading!