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designing and building with wood channels my creativity and challenges my mind.
This blog is a record of my life in my studio.

Wednesday, November 10, 2010

When it absoutely, positively, has to be black...

I was recently asked to make some custom aquarium cabinet stands.  Apart from having to support over 1,000 pounds, my customer also wanted one of the stands in black.  Needless to say, I was more concerned about the weight-bearing capability of my cabinet design than I was about the finish.  Turns out, getting a good black on wood is more difficult than it seemed at first.  After a few failures and a lot of experimenting, I have a few methods for getting a deep, rich black.  I also have a few general tips on finishing in black in general. 

Normally eschewed by woodworkers because it obscures the natural beauty of the wood, staining can be the only option for a piece.  For example, since the star of the show in my project is the coral reef aquarium, the stand should be unobtrusive.  Hence the black.  But since I've learned more about making wood black, I've come to respect it as a finish, and I plan to use black finishes in my future pieces.  Anyway, on to the lessons!

Lesson 1: Finish all pieces separately.  This is a basic rule for finishing in general, but I mention it because when finishing in black, some special problems come up.  The question is: when in the finishing process to assemble?  Obviously, assembly occurs after you stain or paint.  But should you apply a topcoat before assembling?  What if there's a barrier coat, such as shellac, between your pigment layer and your topcoat?  At the moment, I favor going all the way to the first layer of topcoat before assembly.  The danger is if you accidentally sand through the pigment after the case is together.  If you do, you might have trouble patching the hole.

Lesson 2: water-based stain is better than oil-based.  At least when it comes to black.  Water based ebony stain is the consistency of jelly, and forms a thick coat of pigment on the wood.  The grain still shows through, but this stuff is one-and-done when it comes to coats.  I found oil-based ebony stain to require several coats for deep black on birch and maple, or else just soaking the wood in stain so much I worried I'd warp my pieces. 

Lesson 3: use barrier coats of wax-free shellac.  Something has to set the pigment in the water-based stain, and thin, wax-free shellac sanding sealer does the trick well.  It dries so fast there's not much chance of upsetting the pigment, and with a quick brush you can get a very smooth barrier layer over your pigment.

Lesson 4: Pitch Black Glaze deepens the finish.  Glazes are water based, translucent colors that are used for all sorts of effects.  In this case, I use Jet Black glaze over shellac over pigment stain to give the finish added depth.  In between coats, I rub out the brush marks with 0000 steel wool.

Lesson 5: Any topcoat works well...as long as you use a barrier.  I put a barrier layer of shellac (wax-free, again, for clarity and compatibility) between the glaze and my topcoat.  For my first black doors using this sequence, I chose to use satin polyurethane.  It flowed well over the shellac barrier, and the finish was deep, black, and perfect!

General tips:
Brushes: I ended up using brushes rather than cloths for most of these steps.  I found that with a good brush and light strokes, I could get a good flat finish.  The exception was the last coat of urethane, which I padded on with a cloth, then polished.  I spend $30 on a brush.  they don't drop hairs.  they're made of badger hair, and are from Germany.  A Purdy will not cut it.  one hair is too much.

Mixing water-based and oil-based layers:  Shellac (100% wax free) is compatible with almost every finish.  therefore, if you use it as a barrier, you can use any combination.  If you work the shellac too much on a water-based layer, you may start to pick up the under-layer.  So be quick with the brush and get a smooth layer on.

Shellacking: I start at the edge, then quickly brush into the piece along the grain, being sure not to leave any thick deposits along the edge.  I work around each edge to the middle.  If the middle isn't covered after all four edges have been done, I strike a line of shellac across the grain in the middle, then work it out along the grain to fill in the bare area.  Going back to get rid of a lump of shellac is hard to do cleanly.  better to leave no lumps in the first place.

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