Opacity in a pigmented system is controlled principally by
Answer: A
Scattering rather than absorption prevents light reaching the substrate. Two constant theory handles the two coefficients independently. Scattering rather than absorption gives opacity. The two coefficients act independently.
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Consider the following statements about pigmented systems.
1. Scattering governs opacity and hiding power.
2. Absorption governs the hue and depth of the colour.
3. A single coefficient describes both adequately.
Answer: B
Correct answer: 1 and 2 only
Statements 1 and 2 separate the two optical roles: scattering, largely from the white pigment, determines opacity and hiding power, while absorption determines hue and depth. Statement 3 is precisely why single constant theory fails for pigments - the two must be modelled separately, which is what two constant theory does.
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Fluorescent colourants complicate recipe prediction because
Answer: C
Ordinary Kubelka Munk theory has no term for emission at all. Special treatment and careful ultraviolet control are both required. Ordinary theory has no emission term at all. Extended models are required for fluorescence.
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Assertion (A): Standard Kubelka Munk theory cannot handle fluorescent colourants.
Reason (R): It describes absorption and scattering but contains no emission term.
Answer: D
Correct answer: Both A and R are true, and R is the correct explanation of A
Both are true and the reason gives the mechanism. Kubelka Munk accounts for light absorbed and light scattered, and a fluorescent colourant does something neither describes: it absorbs at one wavelength and re-emits at a longer one, so more light can leave at that wavelength than arrived. Handling fluorescence requires a bispectral treatment relating excitation to emission.
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A colourist would reject a predicted recipe that
Answer: A
Correct answer: uses a dye with inadequate fastness for the end use
Fastness is outside the colour calculation altogether - the software matches the shade and knows nothing about how it will survive light and laundering. A recipe that is correct colorimetrically and unfit for the end use is exactly the case the colourist exists to catch. A metamerism index of zero, by contrast, is an argument for the recipe rather than against it.
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Three of the following can be computed by matching software from its database. Which is the odd one out?
Answer: B
Fastness is a chemical property not derivable from reflectance data. The other three follow directly from the stored spectral and price information. Fastness requires separate testing. Reflectance data cannot reveal it.
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The reflectance of a dyeing at a given wavelength depends on
Answer: C
Correct answer: the sum of the K over S contributions of all the colourants present
\[ \left(\frac{K}{S}\right)_{mixture} = \left(\frac{K}{S}\right)_{substrate} + \sum_i c_i \left(\frac{K}{S}\right)_i. \] The reflectance is then recovered from that sum. Additivity in \( K/S \) rather than in reflectance is the single assumption on which the whole method rests.
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Arrange the steps of a recipe prediction calculation in order.
1. convert each candidate back to reflectance
2. measure the standard and convert to K over S
3. rank the candidates on cost and metamerism
4. search combinations of database colourants
Answer: D
Correct answer: 2 - 4 - 1 - 3
The calculation proceeds in the transformed domain and returns at the end. The standard is measured and converted to \( K/S \) at each wavelength; combinations of database colourants are searched for concentrations summing to that; each candidate is converted back to a reflectance curve; and the candidates are then ranked on cost, metamerism and the other practical criteria.
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The search for candidate recipes is carried out in K over S space because
Answer: A
Searching in reflectance would require solving a non-linear system. The transformation turns the problem into a tractable linear one. Reflectance would require a non-linear solution. The transformation makes the search tractable.
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Colour matching software can fail badly when
Answer: B
No combination can reach a colour outside what the palette can produce. The software should report the shortfall rather than offering a poor recipe. No combination reaches outside the gamut. The shortfall should be reported honestly.
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