This test describes the visual determination of essentially light coloured liquids (yellow scale) based on the ASTM test method D1209. This test is commonly referred to as APHA colour or platinum-cobalt (Pt-Co) colour.

In order to achieve a typical “methanol” standard wall wash, it is usually required that the colour is less than 10, but in a growing number of cases, the specification is maximum 5 which is effectively no visible discolouration.

EQUIPMENT

• 100 ml Nessler tubes / glass measuring cylinders.
• ASTM D 1209 (APHA colour) Pt-Co colour standards. Typically 20 / 15 / 10 / 5.
• Laboratory grade methanol

PROCEDURE

Fill a Nessler tube with 100 ml of the wall wash sample. Fill a second Nessler tube with 100ml of pure laboratory Methanol (reference sample). Look down the length of each tube against a clean white background and compare the reference sample against the wall wash sample. Any difference in colour signifies that the wall wash sample is discoloured.

RESULT

Prepare a range of platinum-cobalt colour standards as described in ASTM D1209, bearing in mind the wall wash specification that has to be achieved.

If the maximum colour specification of the wall wash sample is 10 APHA, simply compare the prepared 10 APHA colour standard directly against each wall wash sample in turn. If the wall wash sample has less colour than the 10 APHA standard, it can be reported as having a colour of “less than 10 APHA”.

If the wall wash sample has more colour than the 10 APHA standard, it will fail to meet the required specification and should be reported as having a colour of “greater than 10 APHA”.

In order to identify the precise colour of the wall wash sample, it will need to be compared against increasingly higher colour standards until it is found which colour standard the wall wash sample is less than.

Note

In the event that no colour standards or spectrometer are available on board, compare the wall wash sample against pure methanol. If the test specification is 5 or 10 APHA, there should not be any visible discolouration of the sample. If there is, the sample will most likely fail to meet the required specification.

The Pt-Co colour scale is based on a yellow colour, but wall wash samples may contain other colours, the presence of which will almost always cause the wall wash sample to be rejected.

Colour scales

Below are examples of the most common colour scales. More details about colour.