Potato dextrin is a starch resist. The advantage of a starch
resist is that it is non toxic,
environmentally friendly and fairly inexpensive. Dextrin has
no harmful fumes like wax, and doesn't
have the same burn or fire potential.
This process has barely been used and there is wide open
territory to experiment. In fact this is true
in most areas of surface design.
Potato dextrin produces a very wide range of textures with a
great deal of repeatability. Dextrin can
be used on cotton, wool, silk, thin fabrics and even
velvet. Each fabric type produces a different
range of results.
Working with dischargable black 100% cotton fabric, stretch the
fabric on a styrofoam batt,
securing it with T-pins approximately every 1 inch around the
entire perimeter of the fabric. An
even tight stretch is best for initial experiments. This is
similar to stretching a canvas for painting or a
screen for screen printing.
I mix the dextrin by weight exactly, 1 to 1. I add 1 pound of
dextrin to 1 pound of water at nearly a
boil, and stir until I have lumpless white potato gravy. TIP:
Add dextrin to water, not water to
dextrin. I use an electric hand mixer. For those without
scales, add 1 1/3 cups of dextrin to 1 cup
of boiling water.
I mix between 1-3 pound batches depending on what I'm trying to
accomplish. A pound will cover,
depending on thickness and your design .5 to 2 square
yards. These are very broad guidelines,
coarser fabrics require more dextrin than thin fabric. We have
found that less than boiling water
works too, but you need to be quicker and more efficient about
As the hot dextrin cools it thickens, stir occasionally to keep
lumps from forming. Somewhere
thicker than honey is where application is recommended,
approximately body temperature. This
too has many variables, the temperature at application will
affect the result too.
The dextrin is brushed, or squeegeed onto the fabric and allowed
to cool/dry. As the dextrin cools
it cracks and depending on it's thickness, temperature,
humidity, and probably the moon, the cracks
develop differently. There are many variables, I often say
"everything affects everything" and it is
especially true with potato dextrin.
The coating can be super thin to a quarter of an inch
thick. In general the thinner coating yields the
smaller, finer crackle. Too thin and the bleach will eat
through, too thick and the crackle won't
form. You will need to find the right balance/combination
between thickness of dextrin and how
much bleach you spray onto it. If the dextrin is too thin it
will not resist the wetting melting action of
the bleach, it will melt/eat through the dextrin.
While the dextrin cools/dries it becomes milky white. You can
scrape or stamp into the semi soft
dextrin. Different line qualities are possible depending on how
stiff the dextrin has become when you
stamp or scrape.
Pardon my vagueness....
"At some point" you apply bleach to discharge or strip away the
color. The point at which this is
done is truly one of observation. As the starch dries it curls
and peels up away from the fabric.
When the starch gets too dry it pops off of the fabric. The
optimal point to apply bleach is when the
dextrin has dried as much as possible without popping off due to
over-drying. If I put an all-over
coating on the fabric and strove for evenness, it still would
come out slightly uneven. The cracks
would develop faster where the coating was thinner. I have
learned by experience and careful
watching what the cracks should look like when I apply the
bleach. If the piece is cracking
unevenly, you take the best compromise.
Taking full safety measures (protective clothing, rubber gloves,
eye protection and acid gas
respirator) and working outdoors, spray bleach lightly onto the
cracked surface and between the
cracks. When the color of the fabric seen in the cracks
lightens sufficiently, stop the process by
flushing with cold water to remove the strong bleach.
Different blacks bleach to different colors, it is a process of
learning what each will do. Blacks can
bleach to yellow orange, orange, red, tan, green, and the blacks
that we use bleach to nearly white.
If the fabric is exposed to the bleach too long it will eat the
fabric, so one needs to learn when to
stop and not wait for more color change. The color usually
lightens more during the rinse and dry
Unpin fabric from batt and rinse again in cold water rinsing off
more bleach and some of the dextrin
by folding and scrunching the fabric in a bucket or tub of water.
To remove all remaining dextrin and excess bleach, wash the
dextrin-covered fabric in the washer
with cold water. Continue to rinse in warm, and then hot soapy
water. Rinse to remove soap,
treat with Anti-chlor to remove all traces of bleach, dry and iron.
If dextrin pieces collect in the bottom or sides of the washer
just scoop them up and into the trash.
That is a good starting point, it is like grandma teaching how
to make scratch pie crust without a
recipe, you need to try, feel, see, try again till your hands
and eyes recognize the correct qualities.