IB. 109
Useful products from phytophagous insects
Silk
Exercise 1--Reeling silk.
In this exercise, you'll reel silk from a cocoon of Bombyx mori, the Japanese silk moth.
Take a cocoon and place it in boiling water, turning it over several times. Turn the heat down
and allow the water to cool enough so that you can handle the cocoon. Brush the outside of the
cocoon to loosen stray silk strands. Remove these stray fibers, lifting the cocoon up out of the
water occasionally by these fibers. Repeat this process until, instead of several loose ends, all
you see is a single fiber. Wind up this fiber on an applicator stick or a pencil. This filament is
raw silk and may be up to 1300 yards long. Can you tell that this fiber is actually a double
strand?__________
Why is the filament double stranded?_______________________________________________.
One thing to remember--be patient and gentle--don't rush!
Exercise 2--Identifying silk fabric
Nowadays, with so many synthetic fibers available, it's often difficult to tell at a glance
what sort of fibers a particular fabric has been made from. Textile chemists have a simple test
for distinguishing between plant or synthetic fibers from animal fibers (such as silk or wool).
Whereas plant or synthetic fibers are based on cellulose, a molecule made up only of carbon,
hydrogen, and oxygen atoms, animal fibers are made up of protein, which consists not only of
carbon, hydrogen, and oxygen atoms but also nitrogen and sulfur atoms. When animal fibers are
burned, they give off a distinctive sulfurous odor; in contrast, plant or synthetic fibers (such as
rayon) simply smell like burning wood or paper (which is also made of cellulose). Another
difference between synthetic and animal fibers is that, when animal fibers are burned, they
become brittle and break up easily into dust; when synthetic fibers are burned, they melt and
form a hard ball.
For this exercise, cut a small square from the fabric of a silk tie, a wool tie, a linen, a
rayon, and a polyester tie. Light a match and place it to one end of the fabric swatch. Compare
the rate at which the fabric burns and also compare whether or not the fire extinguishes itself.
Which burns fastest?
Which (if either) extinguishes itself?
Which burns with a sulfurous smell?
Now feel the burned section of swatch. Which ties, when burned, crumble into dust?
Which ties, when burned, form a hard ball?
Now cut a swatch from a tie that is not marked as to what it's made of. Examine the way it looks
and feels and compare it to the marked ties. What do you think it's made of?
Try the burn test. What are your conclusions based on the burn test?
Display
Life stages of Bombyx mori: eggs, first instar, ultimate instar, pupa in cocoon, adult
Other species of moths (Saturniidae) and their cocoons.
Why do you think these species are not used extensively for silk production?
Products made with silk protein
Dyes
Display
Scale insects
Shellac
Flake lac
Products colored with insect pigments (cochineal)
Cochineal scale
Exercise 3. Dyeing with cochineal
Cochineal can be purchased from arts and crafts suppliers (2004 prices are about $70 per pound,
from Earth Guild, Asheville, NC). Take a look at one of the insects under the microscope and
see what anatomical features are distinguishable.
We're using 25 g cochineal per liter of water in the dye. Soak the cochineal for one hour in warm
water (one ounce cochineal/one ounce wool or cotton). Boil the insects for fifteen minutes, then
strain with cheesecloth to remove bodies, and pour the strained liquid into a container (dyebath)
adding water to reach 4 gallons.
A mordant is a chemical that impregnates fibers and causes an insoluble complex to form with
the pigment, thereby rendering the dye "fast". Most mordants are either mineral salts involved in
the complex or alter the pH of the dye solution. The choice of mordant can affect the color and
intensity of the dye as well. A caution: many excellent mordants are also highly toxic mineral
salts. For your safety, we will use mordants with low toxicity in our dyeing. Nonetheless,
PLEASE BE CAREFUL IN HANDLING ALL MATERIALS!!
We will use four different mordants with the cochineal dye: ferrous sulfate (mineral salt), alum,
tannic acid, and thio-urea dioxide. All of these mordants have had cream of tartar added to them
to give a more even color.
1. Pre-wash cloth and rinse .(before class)
2. Pre-soak cloth for 15 minutes in warm soda (alum) water.
3. Remove cloth and apply ties and twists to wet cloth.
4. Apply dye with pipettes.
5. Apply mordants to dyed areas with pipettes.
(TA will do the following steps)
6. Allow cloth to sit overnight so that the dye can thoroughly impregnate the fibers.
7. Undo ties, rinse in hot water, and wash in boiling, soapy, salt water (20 g table salt per liter
water) for one hour.
8. Rinse in cool water and hang out to dry.
The use of hot, salty water in step 7 further fixes the dye onto the cloth and removes unbound
pigment complexes. Failure to "fix" the dye results in leaching of the cochineal - possibly onto
you or your clothes! We suggest that you wash the cloth by itself in hot water until it no longer
bleeds.
What color is fabric dyed with unmordanted cochineal?
What does the mordant alum do to the color?
Tannic acid?
Ferrous sulfate?
Thio-urea dioxide?
Exercise 4. Products from galls
Many different species of insects are capable of invading plant tissue and causing abnormal
growth; these so-called "galls" often contain exceedingly high concentrations of certain
distinctive plant chemicals. Among these are tannic acid and gallic (from "gall") acid. These
compounds have two chemical properties that make them very useful; they form complexes with
proteins (and thus can be used to tan leather) and they complex with iron salts to form colored
compounds (that can be used as inks).
4a. A 2% tannic acid solution (500 mg/25 ml water) has been prepared and mixed with a few
drops of a 10% sodium chloride solution. Pour 3 ml of this tannic acid/salt solution into a test
tube. Add 4 or 5 drops of the 1% gelatin solution (gelatin is a protein). Does a precipitate form?
Why do you think that tanning leather (complexing proteins in animal skin with tannic acid)
would be a useful thing to do?
4b. Pour 3 ml of the tannic acid/salt solution into another test tube. Add 3 or 4 drops of a ferric
chloride solution (9 g/100 ml) to the test tube. What color precipitate forms?
Try dipping a paintbrush or pen point into the reaction mixture and using it as ink. What
happens?
Next , add 3-4 drops of gum arabic solution to the test tube and mix thoroughly. Then dip the
paintbrush again and use the mixture as ink. Is there any difference?
What do you think gum arabic does?
4c. Examine the various galls on display. What plant families are represented in the display?
Do gall shapes and sizes vary with plant species?
The Dye Process
Entomology 105 - Useful products from phytophagous insects
We're using 25 g cochineal per liter of water as our dye source.
A mordant is a chemical that impregnates fibers and causes an insoluble complex to form with
the pigment, thereby rendering the dye "fast". Most mordants are either mineral salts or
compounds that alter the pH of the dye solution. The choice of mordant can also affect the hue
and intensity of the dye. A caution: many excellent mordants are also highly toxic. For your
safety, we will use mordants with low toxicity in our dyeing.
We will use four different mordants with the cochineal dye.
1) ferrous sulfate (mineral salt) produces greens and golds.
2) alum lightens cochineal to pink.
3) tannic acid darkens cochineal to purple and black.
4) thio-urea dioxide produces deep blues.
Protocol
1. (before class) Pre-wash cloth and rinse.
2. Pre-soak cloth for 15 minutes in warm soda water.
3. Remove cloth and apply ties and twists to the wet cloth.
4. Apply dye with pipettes.
5. Apply mordants to dyed areas with pipettes.
(TAs will do these steps)
6. Allow cloth to sit overnight so that the dye can thoroughly impregnate the fibers.
7. Undo ties, rinse in hot water, then wash in boiling, soapy, salt water (20 g table salt per liter)
for one hour.
8. Rinse well in cool water and hang out to dry.
The use of hot, salty water in step 7 further fixes the dye onto the cloth and removes unbound
pigment complexes. Failure to "fix" the dye results in leeching of the cochineal - possibly onto
you or your clothes! We suggest that you wash the cloth by itself in hot water until it no longer
bleeds.
Generally, cloth or yarn is pre-mordanted before it is dyed; a mordant is a chemical (often a
mineral salt) that impregnates fibers and causes an insoluble complex to form with the pigment,
thereby rendering the dye "fast." The choice of mordant can affect the color and intensity of the
dye as well. Mordants available for this exercise include: alum (potassium aluminum sulfate),
ferrous sulfate, tannic acid, and thio-urea dioxide. To dye with cochineal, soak the cochineal for
one hour in warm water (one ounce cochineal/one ounce wool). Boil the insects for fifteen
minutes, then strain with cheesecloth to remove bodies, and pour the strained liquid into a
container (dyebath) adding water to reach 4 gallons.
Soda water: 1 cup soda in 2 1/2 gallons water
Directions:
1. Pre-wash cloth in soapy water and rinse.
2. Pre-soak cloth for 15 minutes in soda water.
3. Remove cloth from soda water and apply ties to wet cloth.
4. Apply dye with pipettes.
5. Allow cloth to sit for up to 6 hours or overnight.
6. Undo ties, rinse, rinse repeatedly in boiling soapy water
What color is unmordanted fabric dyed with cochineal?
What effect do the various mordants have on the color of cochineal-dyed cloth?
Ent 105 - Herbivore products lab
Materials list
Cocoon unraveling
forceps
600 mL open beaker
burner
silk cocoons
Tie dyeing
cochineal insects
mortar and pestle
mordants
ferric chloride
rubber bands
cloth
yarn
Tie burning
ties
matches
scissors
Gall ink
tannic acid
sodium chloride
test tubes
gelatin packets
paint brushes
Displays
Bombyx mori display case
shellac display
scale insect display
Foods with cochineal
Ruby Red pink grapefruit
Swiss Formula silk hair conditioner