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by Chris A. Paschke, CPF GCF CMG
"Digital Canvas Test:
Stretched - Abridged"
August 2008
In an effort to make
the stretching and framing of digital canvases a little more predictable, I
have begun a series of testing in an attempt to try to determine the causes and
control of sagging of these stretched canvases. This article is an abridged
version of the first part of a recent canvas test, with the full Phase One
report currently available - along with spreadsheets of actual test results -
on the PFM website.
Test Basics
The test has been on-going over the past year with Phase Two and Three
on-going through the end of 2008 into 2009. Assorted cotton and poly blend
canvases were printed on HP, Canon, and Epson wide format printers under
manufacturer specs of 60F-80F at 40-60% relative humidity (RH) (photo 1). Phase
One tested both gallery wrap (photo 2) and standard stretched (photo 3) digital
canvases in an attempt to target the causes of sagging. Theories include:
canvas weight; cotton vs. poly/cotton fabric content; swellable vs. porous
receptor layer; dye vs. pigmented inks; and reactions to temperature and
humidity.
The two most
common problems associated with digital canvases include sagging and cracking.
There is a higher perceived value for images on canvas over the same image on
fine art paper, and since canvases are
traditionally stretched, most consumers prefer them framed that way. Test
results showed that sagging occurred at various times, under various conditions
and with various materials, often regardless of temperature or humidity; size
of art; weight of canvas; or type receptor coating.
Ink Receptor Layers
Inkjet canvas must
be coated with a treated surface layer allowing it to receive inks without
bleeding. There are two basic receptor layers: swellable, designed for use with dye inks; and porous, designed for use with pigmented inks.
Swellable ink receptor layers - also called polymeric
or nonporous coatings - are slow dry,
moisture and humidity sensitive, relatively lightfast, and fairly resistant to
gas fading pollutants. These produce inkjet images with a heat sensitivity that
should be cold mounted.
Swellable layers
are made of organic gelatin like polymers that surround and encapsulate the ink
when it hits the canvas surface. The receptor layer then swells from the
moisture in the ink from two to three times its original thickness as it absorbs
(diagram 1). Once it has dried it returns to its original thickness while
encapsulating the ink droplets. The
swelled, puffed up coating is the reason it takes longer to dry once printed,
and in turn is what makes them more lightfast than porous receptor layers.
Swellable canvases for dye inks in the test were InteliCoat Torino 20G and
Torino 21G.
Porous ink receptor layers - also
called microporous and nanoporous - are fast drying and moisture resistant, but
are considered more prone to gas fading pollutants and very susceptible to
scratching and scuffing. Originally designed for use strictly with pigmented
inks, these coatings adapt well to printing of both dye and pigment inks on
canvases. These produce inkjet and wide
format images that are totally heat tolerant. Because of the nature of the
surface ink saturation, they are marketed as quick or instant dry, as the
surface may be lightly touched without damage immediately after printing.
Porous layers
consist of tiny particles glued together with air spaces between them that
spread the ink out evenly penetrating through the top layer down to lower
layers within the coating (diagram 2). When the ink dries, an embedded layer of
colorant remains within the coating. Porous canvases used in the test included:
InteliCoat Torino 20M, 21M, 17M, and Decor; Epson PremierArt WR; Fredrix Inkjet
Canvas; Crane Museo Maestro Canvas-WR (water resistant); and HP Collector Satin
Canvas, Collector Canvas, and Professional Canvas Matte.
Liquid Laminates, and Cracking
The application of
a liquid laminate to a canvas surface increases water resistance; adds to the
UV
protection; and
helps control cracking, splitting and flaking if receptor layers and inks. That
said, it needs to be stressed that a framer should never consider applying any
liquid laminate or spray to any digital image. Only the artist, photographer,
or printer is allowed to apply a laminate.
Oil and acrylic
paintings are originally painted onto a primed canvas that in most cases is
already stretched. The original paint may crack with age with time and the
canvases may indeed sag, but rarely overnight. Since digital canvases are
stretched after printing, the cracked ink occurs immediately when it is bent or
folded at the edges or corners allowing the dried ink and receptor layer to
split revealing the uninked canvas below the surface. Liquid coatings may allow
the inked surface greater flexibility during stretching that could prevent
corner splitting or flaking at the staples.
Sagging
Sagging can be an
issue at with any sized canvas, even small ones. I recently viewed a small
9"x12" nicely taut, newly stretched, inkjet canvas at a frame shop in
South Dakota at 9am with a temperature of 80F at 75%RH. That same afternoon it
had relaxed to a very sloppy, saggy canvas with the temp at 100F and the same
75%RH. Phase One recorded positive results of tight to taut canvases at both
70%RH and 10%RH, but not all canvases. It appears humidity does play a part,
but it is temperature fluctuation, humidity, canvas quality, and the other
materials used that all determine if a canvas will sag.
Liquid laminates
do not appear to have much effect on the issue of sagging. The most consistent
canvases seemed to be the ones with a matte finish (photo 4), and were not
marketed as water resistant. HP Professional Canvas Matte scored the best
across the board, as a poly blend, mid-weight canvas with porous layer designed
for pigmented ink (photo 5). Plus all canvases faired well between 50-70F at
30-50%RH. So low, cool temperatures at lower to mid humidity combinations are
best.
Conclusions
Since a framer is
ill-advised to apply any liquid laminate to a digital, they are not included in
this test. Oversized canvases are also not included, but as reported even a
small 10x10" will sag under the right conditions. So far test results
continue to be all over the chart. It does not appear to be the thread, weight,
coating, or ink type that determines sagging. It does appear that high
temperature, high humidity locations such as Hawaii, Illinois, Texas may need
to consider alternative mounting methods for digital canvases. HP recommends
misting the back of their canvas after stretching, but with an aqueous ink that
might be risky.
In a beautiful
65F, 50%RH temperature controlled gallery inside a 10-story building in Las
Vegas last January there were numerous oversized canvases that looked fabulous.
But there were also quite a few 6'x10' canvases that were so sloppy they waved
as you walked by. As I studied the saggy canvases the sales person came by and
asked if I liked the art and if I had any questions. I asked about the loose
canvases and was told their framer didn't know how to properly stretch a giclée
so they had to let him go. Poor framer, not even his fault.
There are no easy
answers. In order to feel secure with the extended-term display choices for
digital canvas, a new tolerance and acceptance of stretching and/or mounting
options may need to be embraced by framers and galleries as well. Education is
the key.
END
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