A Guide to Path Length by Colour Scale

Grading techniques are widely used to assess product colour by comparison with a representative series of fixed colour standards.

Path length is important as the same material measured in different path length cells will appear a different colour. An example of how path length directly effects colour can be found here.

A specific path length of cell must be stated for accurate colour communication.

The measurement standards issued for some colour scales require specific path length cells. Details of the path lengths required for some of the more common colour scales are given below:

PFX/PFXi 880, 950, 995 Series

Scale [recommended path length]
AOCS-Tintometer [1" or 5 1/4"]*
ASTM Colour (ASTM D1500) [33mm]
Beta Carotene [10mm]
Chlorophyll A & B [10mm]
European Pharmacopoeia [40mm]
FAC [10mm]
Gardner [10mm]
Hess-Ives Colour Units [10, 25 or 50mm]*
ICUMSA Colour [100mm]
Iodine Colour [10mm]
IP Units [6"] (reported as for 18" cell)
Klett Colour (blue filter KS-42) [40mm]
Kreis Value [1/16" to 6"]
Lovibond RYBN [1/16" to 6"]*
Pt-Co/Hazen/APHA [100mm]
Saybolt Colour [100mm]
US Pharmacopoeia [40mm]
CIE Values [Depends on sample colour]

PFX/PFXi 195 Series

Scale [recommended path length]
ADMI [50mm]
ASTM Colour (ASTM D1500) [33mm]
Chinese Pharmacopoeia [10mm]
EBC/ASBC [10 or 25mm]*
European Pharmacopoeia [40mm]
FAC [10mm]
Gardner [10mm]
Hess-Ives Colour Units [10, 25 or 50mm]*
Honey Colour (Pfund equivalents) [10mm]
ICUMSA Colour [50mm]
Iodine Colour [10mm]
Klett Colour (blue filter KS-42) [20 or 40mm]*
Rosin US Naval Stores [7/8" Rosin cell 302980]
Series 52 [Depends on sample colour]
Pt-Co/Hazen/APHA [50mm]
Saybolt Colour [50mm]
Yellowness Index [10, 25 or 50mm]*
US Pharmacopoeia [40mm]
CIE Values [Depends on sample colour]

Model F Variants

Scale [recommended path length]
AOCS-Tintometer [1" or 5 1/4"]*
Lovibond RYBN [1/16" to 6"]*

If a different path length, from that recommended above, is used when utilising a colour scale it is critical that this is recorded and communicated to all parties concerned.

*Path length used must be specified when providing values.