Scraping – PZC Chatometry

What surface quality does scraping provide? Come and have a look here and see what chatoyance you can get.

Our sincere thanks go to Ed Harman, who kindly carried out a high-quality scraping operation.

For each of 12 different species, 2 samples were collected and scraped. Both had their chatoyance measured in the as-scraped condition. Then sample 1 was sanded to increasing grits measuring chatoyance at each step, up to 10`000 grit. Finally, these samples got coated with two medium shellac layers. Sample 2 was directly coated with one medium shellac layer. Table below summarizes the results:

Scraping generally appears equivalent to sanding up to 1000÷1500-grit.

When comparing the final finished surface, it appears that results are generally slightly better with 10’000-grit sanding, although Spanish Cedar, Sumac and FS London Plane show an opposite comparison.

Ziricote – scraped + 2 shellac coats – PZC = 9.9

Ziricote – sanded to 10’000-grit + 2 shellac coats – PZC = 10.9

Black Walnut – scraped + 2 shellac coats – PZC = 27.3

Black Walnut – sanded to 10’000-grit + 2 shellac coats – PZC = 28.9

Spanish Cedar – scraped + 2 shellac coats – PZC = 22.7

Spanish Cedar – sanded to 10’000-grit + 2 shellac coats – PZC = 18.8

Euro Maple – scraped + 2 shellac coats – PZC = 21.5

Euro Maple – sanded to 10’000-grit + 2 shellac coats – PZC = 23.9

Sweet Cherry – scraped + 2 shellac coats – PZC = 18.3

Sweet Cherry – sanded to 10’000-grit + 2 shellac coats – PZC = 18.6

Staghorn Sumac – scraped + 2 shellac coats – PZC = 40.1

Staghorn Sumac – sanded to 10’000-grit + 2 shellac coats – PZC = 39.2

Movingui – scraped + 2 shellac coats – PZC = 19.4

Movingui – sanded to 10’000-grit + 2 shellac coats – PZC = 22.8

Black Locust – scraped + 2 shellac coats – PZC = 25.7

Black Locust – sanded to 10’000-grit + 2 shellac coats – PZC = 26.1

QS London Plane – scraped + 2 shellac coats – PZC = 18.5

QS London Plane – sanded to 10’000-grit + 2 shellac coats – PZC = 18.6

FS London Plane – scraped + 2 shellac coats – PZC = 16.2

FS London Plane – sanded to 10’000-grit + 2 shellac coats – PZC = 13.5

Padouk – scraped + 2 shellac coats – PZC = 25.7

Padouk – sanded to 10’000-grit + 2 shellac coats – PZC = 26.1

Sapele – scraped + 2 shellac coats – PZC = 27.9

Sapele – sanded to 10’000-grit + 2 shellac coats – PZC = 28.0

Want to know more? Get Woodworker’s Guide to Chatoyance!

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