Frosting/graining – Horology student

The balance cock is untreated, the barrel bridge is frosted with a small texturing wheel, the gear train bridge is frosted using Aluminium Oxide compound 80 grit

Frosting or graining is the surface finishing that can be seen on many old English watches and has now made a comeback in high-end watches. For me, it’s great advantage is that it does not require specialized machinery.

A good overview of frosting techniques can be found in this article by WatchesbySJX.

Frosting creates a rough surface that is not too reflective and therefore offers a perfect contrast to polished bezels. It can be achieved by at least 3 techniques: sanding (blasting sand on the part with a special machine), with a texturing wheel (only requires a hand-held rotating tool), or with abrasive pastes.

On the left, I used silicon carbide 120 grit, on the right I used aluminium oxide 80 grit

I started by using abrasive pastes as this required the least investment and I liked the idea of creating something without any machinery. I used abrasive pastes, either aluminium oxide (AO) or silicon carbide (SC), on a piece of plexiglass and pressed the piece against it upside down while making circular motions. I found I had more striking results with AO grit 80 than with SC grit 120. However, in both cases I was unable to avoid scratches and it was especially difficult to apply this technique on a part with recesses as the paste would build up in the recesses in the part.

Then, upon recommendation from Christian Lass from learnwatchmaking.com, I tried with loose silicon carbide beads and replaced the plexiglass (too soft) with glass. I used alcohol to create a paste-like texture.

Glass base, silicon carbide mixed with alcohol

I was also careful to use very small gestures to decrease the risk of scratches.

I then moved to texturing wheels and have tried several sizes and levels of coarseness. Small wheels 10mm combined with fine strands gave a satin result where the lines were visible. It was easier to get a uniform surface with coarser wheels, even with a small diameter. However, to have a more dramatic effect, larger wheels (40mm) are better.

From left to right, 40mm coarse, 10mm coarse, 10mm fine

I also found that for smaller wheels a higher number of revolutions per minute (rpm) made it easier to have a uniform surface with no visible lines. Therefore for 10mm wheels I recommend 10’000 rpm, whereas with larger wheels (40mm) 5’000 rpm seems better.