BS ISO 21066:2018 pdf download – Fine ceramics (advanced ceramics, advanced technical ceramics) — Qualitative and semiquantitative assessment of the photocatalytic activities of surfaces by the reduction of resazurin in a deposited ink film
5 Principle 5.1 General A photocatalyst activity indicator ink is deposited, using a K-bar, onto samples, 25 mm × 25 mm square, of the photocatalytic material under test, which have previously been wiped-clean and possibly UV- conditioned. If upon depositing the ink film on the material under test, but before irradiation, the ink changes from blue to pink or colourless, the sample is reactive (usually due to a highly alkaline surface) and the ink test is unsuitable for evaluating the photocatalytic material. Assuming the sample is not reactive and is photocatalytically active, then there are two possible tests the material under test can be subjected to as part of this method: a precursor qualitative test and then, for samples found to be within the applicable range of the test, a semiquantitative activity test. The Rz ink test is an example of reductive photocatalysis based on the photocatalysed reduction of Rz and concomitant oxidation of glycerol in an ink coating  .
5.2 Qualitative test method (three samples) Three identically Rz ink-coated samples of the material under test are exposed simultaneously to UVA light from a defined source (see 6.2), with a defined irradiance (see 6.3), and the colour of the ink on each sample is monitored at regular intervals by eye and/or using a digital image recording device, such as a digital scanner or camera, so as to observe the ink change colour, from blue to pink. This process allows, for each sample, an approximate value of the irradiation time required for this colour change to occur, t end , to be determined, from which an average value, t end,av is calculated. The value of t end,av is used to classify the material under test. If t end,av < 1,5 min, then it is classed as being above the applicable range of the test. If 1,5 min ≤ t end,av ≤ 45 min, then it is classified as being within the applicable range of the test. If t end,av > 45 min, then it is classed as being below the applicable range of the test. If the material is initially classified as being ‘above the applicable range of the test’, then a reduced irradiance shall be used in a re-run of the test. If, using the low irradiance UV light, the material is found to be ‘within the range of the test’, then the semiquantitative test can be run to assess the activity of the material, also using the low UV irradiance. Further details regarding the decision-making strategy employed in this test are given in 9.1.
5.3 Semiquantitative test method (eight samples) This subsequent test method is only used for materials which have been identified previously, using the qualitative test, as being within the applicable range of the test, i.e. samples which exhibit 1,5 min ≤ t end,av ≤ 45 min. In the semiquantitative test method, eight Rz ink-coated samples of the material under test are exposed simultaneously to UVA of a defined irradiance from a defined source, and the colour of each sample is monitored at a regular time interval, Δt (see Clause 4), either using a digital camera or hand-held scanner, until the ink turns pink. RGB colour analysis of the central part of each digital image of the ink film for each sample, for each irradiation time, t, is used to calculate average values for RGB(R) t , RGB(G) t and RGB(B) t , for that time point. A plot of the normalized value of the RGB colour analysis parameter, R t , (see Clause 4) vs. irradiation time, t, is then constructed for each of the eight samples from which the time taken to bleach 90 % of the red component of the image of the ink film on each sample is determined, i.e. ttb(90), along with other key parameters. See 10.3 for further details and for a typical example of an R t vs. t plot for a Rz ink on a photocatalytically active sample. A statistical analysis of the eight ttb(90) values generated by the method, based on the modified score method (see 10.4 and Clause 4), is then used to exclude any outliers. Then, an average value for ttb(90) and associated standard deviation is calculated, i.e. ttb(90) av ± σ, and is taken as an inverse measure of the photocatalytic activity of the material under test.