Stainless steel watch case backs usually have some sort of brushed finish. These finishes look cool, but they are also functional: they are more comfortable on the skin.
A glossy, mirror-polished case back feels sticky. Humidity and sweat create surface tension between the glossy case back and the skin, causing an unappealing glued-on feel. If you wear watches with glass display backs, you know the feeling.
The most popular case back finishes are linear graining—a straight brushing going in one direction—and circular graining, which apply circular brush marks to create a satin finish with an appealing look.
When you tilt the case back, it will catch the light in a propeller pattern and wink at you.
The Straight Word on Circle Finishes
Applying circular finishes is pretty easy. For example, here’s the “pre” version of a Rolex 6420 case back. It has the usual scuffs along with some deep scratches from some inept attempts to open it.
The first step is to polish it as usual to get the metal to a good state. Brushed finishes can obscure nicks and scuffs, but they will be more visually striking when applied to a shiny surface.
This Rolex case back got some attention with a felt wheel and stitched buffs. You don’t need to polish the case back to an absurd mirror shine if you’re going to brush it later, but why not—it’s a slow day.
This mirror-finished case backs look appealing, but it will be sticky when worn. Many Rolexes have a linear grain, but this case back is domed instead of flat. A circular grain would look nice and work with the domed contour.
The principle of circular finishing is easy: you need to spin the case back and then apply an abrasive to it, starting in the center and then working your way out.
I’ve been using a case-back attachment to a Foredom bench polishing lathe. (The lathe post is 8 mm, and the attachment’s recess is 14 mm, so a simple spacer is needed, too. Look online for 8mm couplings used for RC cars if you need one.)
For this case back, I’m using a fine-grit rubber Garryflex block. Just spin the case at a medium-low speed, place the block in the center, and smoothly draw it out the edge.
A dozen or so passes is usually enough—just stop when the circles have a consistent texture from the center to the edge.
It’s easy to get a nice result.
Mixing Your Scratching
I like the rubber abrasive Garryflex blocks and probably use them more than any other abrasive for circular finishes. They give a smooth, even grain to stainless steel, resulting in a silky satin feel. The examples at the start of the post used the coarser blue block.
But different abrasives will give you different results, and different steel case backs respond better to some than others.
A classic option is emery cloth, which is well suited to graining steel.
I usually use a coarse grit. For a more even grain, you can wrap the emery cloth around something stiff, like this India stone file.
Here’s what a Seiko case back looks like afterward. The coarse grit brings out deep, appealing grooves.
Speaking of deep, appealing grooves…
Okay, back to watches.
If you plan to manicure your fingernails after polishing your watch case, you can get great results with cheap emery sticks.
Tips for Excellent Results
Circular finishes really are easier than they look, but a few technique tips will give you better results. This video—possibly the least-viewed video on YouTube, with 16 views at the time I write this—illustrates two good tips.
First, visualize a single line, a radius from center to edge, and move the abrasive along that line. Brushing from center to edge and back again will give a finer, crisper result than moving the abrasive in a circular or up-and-down motion. Notice how the polisher in this video keeps the sandpaper along one radius as the case back spins.
Second, you can get a deeper, crisper pattern by applying a fine edge to the case back. For example, apply just the fine edge of a rubber block to the case back’s radius instead of simply smooshing the block against the case. Likewise, wrap the emery cloth around something firm instead of simply pressing it against the case with your thumb.
Any abrasive pressed to a spinning back will yield a circular pattern, but the circular channels are crisper when you apply a finer edge. Notice how in the video he has wrapped the emery sandpaper around a piece of glass, affording a sharp abrasive edge.
And third, you’ll get better results if the abrasive has some “give.” Rubber abrasive blocks, being spongy, will conform to the case shape, so they’ll give a superior result. The surface of an emery cloth, too, will grind down to conform to the case back.
If the abrasive is too hard, it will skip along the surface, yielding rough spots. For example, you can apply an India stone directly to the case back. It gives a great cut, but it is hard to get a consistent finish. Here’s a Seiko case finished with the India stone.
The graining is striking but uneven: the file leaves gaps between circles and shiny patches around the contoured areas on the rim. Compare to results of a blue Garryflex block on a contoured case back: