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What Is The Percentage Of Graphite To Clay In The HB Pencil Scale?

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Pencils contain graphite & clay, plus some wax (the wax is added for lubrication). 
The chart reproduced below is from :
Sousa MC, Buchanan JW. "Observational models of graphite pencils". Computer Graphics Forum 19.1 (2000): 27-49. P. 30.
Bear in mind that value will vary somewhat between manufacturers (NB - Sousa & Buchanan neglect to indicate which manufacturers they contacted).

"Percentage values of the mass amount of graphite, clay, and wax particles for the entire range of pencil grades based on information received from pencil manufacturers"
pencil # / graphite / clay / wax
9H / 0.41 / 0.53 / 0.05
8H / 0.44 / 0.50 / 0.05
7H / 0.47 / 0.47 / 0.05
6H / 0.50 / 0.45 / 0.05
5H / 0.52 / 0.42 / 0.05
4H / 0.55 / 0.39 / 0.05
3H / 0.58 / 0.36 / 0.05
2H / 0.60 / 0.34 / 0.05
H  / 0.63 / 0.31 / 0.05
F  / 0.66 / 0.28 / 0.05
HB / 0.68 / 0.26 / 0.05
B    / 0.71 / 0.23 / 0.05
2B / 0.74 / 0.20 / 0.05
3B / 0.76 / 0.18 / 0.05
4B / 0.79 / 0.15 / 0.05
5B / 0.82 / 0.12 / 0.05
6B / 0.84 / 0.10 / 0.05
7B / 0.87 / 0.73 (sic.)* / 0.05  [* obviously a typographical error; it should be ~0.7]
8B / 0.90 / 0.04 / 0.05

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