QAs

SC/NATS 1870 – Colour Mixture Assignment Due: Nov 6 2014, 2:30pm

Worth: 15% LATE ASSIGNMENTS WILL NOT BE ACCEPTED

The colour mixture assignment provides exercises in mixing colours subtractively with paint, and additively with spinning disks. It is hoped that by physically mixing paints and performing these exercises, you will have a deeper understanding of the physical and visual nature of colour, and the difference between the nature of these two processes of mixing colours. In addition, you will be sketching spectral reflectance curves for many colours, so a clear understanding of spectral reflectance curves is required prior to commencing these exercises. Written interpretations of the exercises performed are also a component of this assignment.

Painting and optical mixture will be demonstrated in class. Work for this assignment is to be completed on your own time. If you have questions, contact your Professor.

The stapled, hardcopy assignment is due at the beginning of class on Nov 6. Please staple all work together or hand everything in in an envelope (max. size 11x14 inches) with your name and student number clearly labelled on the front. All work for this assignment must be handed in together. Do not hand in work in a binder or plastic folder.

You are expected to complete the painting, optical mixture, and write-ups on your own. Note that copying from another student, using the same painting swatches, or otherwise duplicating results is considered plagiarism and is a punishable offense.

Some exercises also include written answers to questions. These may be attached to the notebook pages, with your name, student number and exercise number clearly labelled. In some instances the written questions are as important as the painting exercises.

Supplies: You will need the following (suggested- acrylic) paints for this assignment: Red, Blue, Yellow (painter’s primares; optional – you may use instead / or in addition the subtractive primaries magenta, cyan, yellow). Make a note of the brand and specific colours used, as each will affect the final mixed colour.

References: Itten, `The Elements of Colour’

Williamson & Cummins ‘Light & Colour in Nature & Art’ (spectral reflectance curves)

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1. Understanding Subtractive Mixture: the Colour Wheel

a) The colour wheel is an exercise in mixing hues. You will construct a colour wheel where 12 colours are arranged in succession through the prismatic hues (i.e. R, RO, O, OY, etc.). Start with the 3 “painter’s” primaries. Mix 2 primaries to obtain the secondaries (i.e. R+Y=O, etc.), and mix a primary and a secondary to obtain a tertiary (R+O=RO, etc.). You may need to experiment with the amounts of each constituent colour to obtain the exact hue you want (e.g. a small amount of R may be required to obtain a satisfactory hue of RO). It is probably best to experiment on a piece of paper, then cut out the best-mixed hues for your final colour wheel. An appropriate size for each hue ‘square’ is approximately 2-3 cm. Make sure that you arrange your hues in a circular format, with adjacent hues overlapping (i.e. – don’t leave spaces between the squares, don’t outline with black or white; you may need to cut your squares into "wedge" format)

b) Sketch a possible spectral reflectance curve for each of the 12 colours on same sheet as colour wheel.

c)

1) cadmium red + ultramarine blue = purple

2) magenta + cyan = purple

Sketch spectral reflectance curves for the above paint colours: 1) cadmium red + ultramarine blue = purple 2) magenta + cyan = purple

d) Describe how the value and saturation of the mixed purple 1) differs from purple 2). What factors in the process of mixing colours subtractively contribute to the difference in visual quality between these two purples [i.e. why is purple 2) ‘better’ than purple 1)]?

2. Understanding Additive Mixture: Spinning Optical Disks

This part involves doing an experiment on optical or visual or additive colour mixture, and writing it up as a scientific report.

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Experimental Procedure: Create a spinning disk for mixing colour visually. The design specifics for the spinning disk are up to you. Step 1: Divide the disk into 3 equal pie-shaped portions. Step 2: Paint (or used coloured card) one portion of the disk red, another blue and the third green. Step 3: Spin the disk and see if white results. Step 4: Record your observations in your logsheet (discussed below). Step 5: If you do not see white in step 3, experiment by varying the proportions, the layout within the disk and/or the precise colours used, until you do see white (or the closest approximation to white). Keep a record of your trials together with the colours seen in your logsheet. You are highly encouraged to experiment as much as you wish. Optional variations: Try with magenta, cyan and yellow; try with different mediq.

Use a logsheet to document your process; suggested format:

Colours in Disk | Proportions of Colour | Additive Colour Mixture Seen

Write up your experiment as follows: 1. Method: describe/document mechanism used to spin the disk.

2. Observations: include your logsheet.

3. Results: Describe how (if) you finally achieved white: proportions, disk layout etc. If you did further experimentation, describe any interesting or significant findings. One additional investigation could be to mix the colours used subtractively, and compare to the additive mixture.

4. Answer the following questions:

a) Theoretically, one would expect equal proportions of R, G, B mixed in this way to yield white. If this was not the case, can you explain why? b) Why did we not choose R, Y and B to mix optically? c) What colour results when magenta, cyan and yellow are mixed optically? Is this a surprising result? d) Are the colours you obtained from optical or additive mixture the same as those mixed subtractively (i.e. does red+green yield the same mixture additively and subtractively?) Why or why not? Explain both mixing processes, and describe why the particular mixed colour results.

In addition to the above, also hand in:

• Your spinning disks used (make ‘pockets’ in you notebook to include the disks)

• A photograph of you performing the experiment Any plagiarized work will automatically receive a grade of zero.

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