Welcome! That is some pretty beefy black walnut! Do you plan to make the top that thick or will you re-saw it? I always use biscuits for the table tops, especially if the top will be pulled open to add a table leaf, heavy loads like stacked books.... The round kitchen table in the photo was the last large table I made and it does open. If you do use biscuits they should be about 2/3 down from the top so as the biscuit dries and shrinks it won't leave a slight depression on the top surface.
Anyway, I've worked with BW quite a bit, one of my favorite woods especially the live edge slabs with crazy figure. I was strictly a polyurethane user on all my table tops until I started using General Finishes Arm R Seal Oil & Urethane. Some of my pieces are in the Gallery and all the live edge pieces have the General Finishes product on them. I prefer the semi-gloss sheen. This stuff is excellent. The oil really makes the grain of the wood pop, which I previously would get using Watco Danish Oil Natural followed by the poly. So that alone saves you a finishing step. It goes on easy with a small piece of old cotton t-shirt or foam brush (light touch) and is self leveling. No water marks from water glasses or spilled wine and is very natural looking. My only knock is that the opened shelf life is relatively short as the product will thicken after a couple months. To extend its life I always pour off what I need into another container, clean the rim of the can and put the lid back on.
Here's my process:
1. Sand to 180 grit. Clean off any dust.
2. Shake the can to mix very well. Pour off what you need.
3. Apply first coat. It might look a little uneven as it soaks into the wood at different rates but no worries. It's also important to not fuss with it once you put it on, don't keep trying to work it as it needs to level itself and starts to thicken. Let dry..
4. Lightly sand with 1000 grit sandpaper to remove any nibs then apply a second coat. Let dry. I apply 2 coats to vertical surfaces and 4 - 5 on horizontal surfaces like table tops.
5. Lightly sand with 1000 grit sandpaper to remove any nibs then apply a third coat to the top. Let dry.
6. Lightly sand with 1000 grit sandpaper to remove any nibs then apply a fourth coat to the top. Let dry.
Good luck. Be sure to post a picture!
Saw Dust Rules
ďIn God we trust. All others bring data.Ē - W.E. Deming
Dave in Rochester, NY