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Worksheet Grade 12 Art & Music

Brisk Hollow pH Color Card: Designing Against Simultaneous Contrast

Grade 12 students diagnose why volunteers misread a fictional creek group's pH color card, then redesign its background, spacing, inks, paper, and labels.

Objectives

  1. Students will identify simultaneous contrast, surface glare, and metamerism as causes of color-matching errors on a printed test card.
  2. Students will specify background, spacing, ink, paper, and labeling changes that make a color comparison card read consistently.
  3. Students will relate the order of the swatches to the chemistry of a two-form indicator dye.
  4. Students will explain their design changes to a non-specialist audience in a short written memo.

Vocabulary

Key words: simultaneous contrast, neutral gray, spot color, process color, gamut, metamerism, specular glare, value

Teacher overview

Volunteer stream groups, pool operators, and many home test kits still read pH by eye: an indicator dye colors the sample, and the reader matches the tube against a printed card. The card is a piece of color design, and its layout, inks, and paper decide how often two readers agree. In this worksheet the fictional Brisk Hollow Creek Watch has printed a card whose readings keep disagreeing, and students work out the design causes and specify a better card. The chemistry that the design has to respect is simple: the dye is a weak acid whose acid form and base form absorb light differently, so every sample shows a mixture of two colors in a proportion set by the pH. The misconception addressed directly is that a printed color has one fixed appearance, so a card will work once the printer matches the ink. The same swatch looks different depending on the colors beside it, the light it is viewed under, and the finish of the paper, and a well-designed card controls all three. Teachers may want a sheet of neutral gray paper and a few colored squares on hand to demonstrate item 1 before students begin.

Brisk Hollow pH Color Card: Designing Against Simultaneous Contrast — Grade 12 Art & Music
Name: ____________________________ Date: ______________

Student Worksheet

The Brisk Hollow Creek Watch is a fictional volunteer group that checks the pH of a local creek every month. A volunteer adds five drops of an indicator dye to a 10 mL water sample in a clear glass tube. The dye is a weak acid. Its acid form is yellow and its base form is red. The sample shows a mix of the two forms, and the mix depends on the pH. The volunteer then holds the tube near a printed card and picks the closest swatch.

In our scenario, the group printed a new batch of cards last spring. Since then, two volunteers reading the same tube have often recorded different values. You have been asked to find the design causes and fix them. Here is the draft card:

  • Eight square swatches, each 8 mm on a side, for pH 6.8, 7.0, 7.2, 7.4, 7.6, 7.8, 8.0, and 8.2. They run from yellow through orange to red.
  • The swatches touch edge to edge in a single row.
  • The row sits on a saturated purple band, which is the group's logo color.
  • Only the first and last swatches carry a number.
  • The card is printed in four-color process (CMYK) on glossy coated paper.
  • Volunteers hold the tube in the air about 5 cm in front of the card and read it wherever they happen to be standing.
  1. A patch of color looks different depending on the colors that surround it. What is this effect called?
  2. The swatches sit on a saturated purple band. Toward which hue will the purple push the appearance of every swatch? Explain.
  3. What background should the redesigned card place behind the swatches? Explain your choice.
  4. Because the swatches touch, each one is seen against two neighbors. Describe a layout change that keeps neighboring swatches from changing each other.
  5. The volunteers hold the tube in the air in front of the card. Describe a change to the physical form of the card that would let the sample and a swatch be seen side by side against the same background.
  6. What paper finish should the redesigned card use for reading outdoors? Explain the problem it solves.
  7. Should the eight swatches be printed as four-color process builds or as premixed spot inks? Explain.
  8. Two volunteers read the same tube. The sample matches the 7.4 swatch in daylight but looks closer to the 7.6 swatch under a warm porch light at dusk. What is this effect called?
  9. Write the one-line reading instruction you would print on the card to control the problem in item 8.
  10. The draft numbers only the first and last swatches. Explain why every swatch should carry its pH number.
  11. Some volunteers have red-green color-vision deficiency. For them, yellow, orange, and red differ mainly in lightness. Describe a quick test the designer can run on a proof to check that these volunteers could still tell neighboring swatches apart.
  12. Every sample is a mix of the yellow form and the red form of the dye. When building the six middle swatches, should the designer follow a straight blend from the yellow end to the red end, or add new hues such as pink or brown to make neighbors easier to tell apart? Explain, using the chemistry described above.
  13. Write a memo of 120 to 180 words to the Creek Watch volunteers. Explain the four most important changes you would make to the card and the reason for each. Write for readers who have never studied color theory.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key
  1. Answer: Simultaneous contrast.
    A color is always seen in relation to its surroundings. The surround pushes a patch toward the opposite, or complement, of the surrounding hue, and it also shifts the patch lighter or darker by value contrast.
  2. Answer: Toward yellow, the complement of purple.
    A purple surround pushes the swatches toward yellow, so the orange swatches look yellower than they are printed and seem closer to the acidic end of the scale. Accept "toward yellow or yellow-green" when the student names the complement as the reason.
  3. Answer: A neutral gray with no hue, of middle to light value.
    A neutral surround adds no complementary shift. A middle value keeps the yellow swatches from looking dark and the red swatches from looking pale. Accept white if the student explains that it carries no hue.
  4. Answer: Separate the swatches with gaps or borders of the same neutral gray.
    When every swatch is framed by the same neutral, each one is seen against identical surroundings and no swatch borrows color from its neighbors. Accept any layout that isolates each swatch on a consistent neutral field.
  5. Answer: Cut a window or slot beside each swatch so the tube sits flush against the card.
    With a hole or slot next to each swatch, the sample and the printed color are seen side by side, at the same distance, under the same light, and against the same gray. Colors compared directly edge to edge are matched far more reliably than colors compared across a gap of air. Accept a slot the tube slides into, a row of punched windows, or a fold-over sleeve with viewing holes.
  6. Answer: A matte finish.
    Glossy coated paper reflects the sky or the sun as a white sheen at some angles. That specular glare washes out the swatch and makes it look lighter and less saturated. A matte coating or uncoated stock scatters surface reflection so the swatch color stays visible from most angles.
  7. Answer: Premixed spot inks.
    Each spot ink is mixed to a formula and printed as one solid layer, so the swatch stays the same from one print run to the next. A four-color build is made of dots of four inks, and small drifts in the press balance change the color. Some saturated orange-reds also sit outside the range of colors, or gamut, that four-color process can print. Give partial credit to a four-color answer that requires a press check against a physical color standard and names the drift risk.
  8. Answer: Metamerism.
    The dyed liquid and the printed ink produce their colors from different mixtures of wavelengths. Two such colors can match under one light and fail to match under another, and warm artificial light is a common cause.
  9. Answer: An instruction naming one consistent light source.
    A good example is "Read in daylight or open shade, with the tube in the window beside the swatches." Accept any instruction that tells the reader to use daylight or a daylight-balanced lamp and to avoid warm or colored light.
  10. Answer: So no reader has to count or guess which swatch they chose.
    Counting from an end swatch in the field leads to errors, especially with wet hands or a crowded card. A printed number also gives readers with color-vision deficiency a second cue that does not depend on hue. Accept either reason if it is explained.
  11. Answer: Convert the proof to grayscale and check that each swatch differs in value from its neighbors.
    Desaturating the file, or copying the proof on a black-and-white copier, shows only lightness. If the eight swatches form an even light-to-dark sequence with no two neighbors looking the same, a reader who sees mostly lightness differences can still separate them.
  12. Answer: Follow a straight blend from the yellow end to the red end.
    A tube can only ever show a mixture of the dye's two forms, so every real sample falls somewhere on the path between the yellow and the red. A pink or brown swatch sits off that path and could never match a sample. The designer should separate neighbors by even steps of value and saturation along the path.
  13. Answer: A plain-language memo naming four changes, each with a correct reason.
    Accept any memo of about 120 to 180 words that names four changes supported by items 3 through 12 and gives a correct reason for each, without technical terms left unexplained. A strong memo might read: "The new card makes four changes so that two people reading the same tube will pick the same swatch. First, the swatches now sit on plain gray instead of purple. Purple makes every color near it look yellower, so the swatches did not show their true colors. Second, each swatch has a gray border and a small window beside it. You can slide the tube into the window so the sample sits right next to the color you are checking. Third, the card is printed on matte paper, so sunlight will not bounce off it and wash out the colors. Fourth, every swatch has its number printed on it, so no one has to count along the row. Please read the card outdoors in daylight or shade, since warm porch lights change how the colors look."

Differentiation

Support

Before students start, run a two-minute demonstration: place identical orange squares on a purple sheet and on a gray sheet and ask which looks yellower. Provide a word bank for items 1, 8, and 11 (simultaneous contrast, metamerism, grayscale, value). For item 13, give a four-row planning table with the headings "Change" and "Reason in plain words" so students draft the memo from the table.

Extension

Ask students to produce the redesigned card as a full-size layout, with swatch size, border width, window placement, type sizes for the numbers, and the reading instruction all specified. Then have them write a one-paragraph press specification for the printer that names the finish, the ink approach, and what should be checked at the press. Students who finish may test their layout by printing it on an office printer and comparing it under daylight and under a warm lamp.

ELL supports

Pre-teach hue, value, background, swatch, and glare using a printed card with each part labeled. Post a sentence frame for items 3 through 7: "The card should use ___ because ___." Allow students to answer items 4 and 5 with a labeled sketch and a short phrase. For item 13, accept a memo written as four numbered sentences, one per change.

Extensions

Students can reproduce a color exercise associated with the painter and teacher Josef Albers: using colored paper, make one orange look like two different colors by placing it on two different grounds, then make two different oranges look alike. Ask them to write two sentences connecting the exercise to the Brisk Hollow card, and to identify which of their redesign decisions would stop the effect from misleading a volunteer.