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Articles
by Chris A. Paschke, CPF GCF CMG
"Mounting Digital Papers"
February 2006
In order to select
the proper mounting technique for any given digital image you must first get to
know up close and personal. Today's 21st century framer needs a more comprehensive
understanding and working knowledge of the composition of printing papers,
their coatings, and the behavior of inks printed on these papers in order to
make the correct decisions about how to mount them. Up until now, heat
sensitivities of digital inks have been linked to thermal dye base inkjet
printers. But recent scientific and use tests have begun to show it is more
likely a paper coating issue and not a technology issue after all.
The Mounting
Debate
During the last
few years Digital Fine Art (DFA), digital canvases, and digital photographs
have become common place artwork for custom framing. Though it is true most any
image may be preservationally mounted using hinges, corner pockets, or edge
strips, more times than not, a digital photo or canvas may actually look better when mounted to a rigid
substrate. Poster images, open editions, on-demand inkjet prints, canvases, and
LE giclees will always be around, and the question of whether or not to mount
them as fine art will no doubt be debated for years to come.
Digital Compared
to Traditional
I have been
teaching about digital printing technologies in relation to framing and
mounting for ten years now, and little by little we seem to have a better
understanding of them. When properly printed and stored, dye-based inkjet and
dye diffusion thermal transfer prints have light stability equal to traditional
photographic C-prints (chromogenic, RC). And over time color toner
electrophotographic and even pigment based inkjet prints have become more stable.
This all makes the framing and display of digital fine art and photos much more
viable., but there still remain issues over heat tolerances when mounting.
New Digital
Thinking
Throughout my five
year affiliation with the photo and digital International Standards Committees
(ISO) we have been working towards developing tests and comparisons to better
understand the world of digital imagery. My own private testing for the framing
industry began in 1996 (Heat Tolerance Test #1) with a study of heat tolerances
of electrophotographic and electrostatic toner copies under dry mount
temperatures ("Digital Heat Tolerances", February 2002).
Then in 2000
(Basic Heat Tolerance Test #2) and 2001 (HP Heat Tolerance Test #3) I ran tests
using an HPdeskjet 960c printer with assorted papers in an attempt to determine
the tolerances of thermal desktop printers with the same mounting adhesives and
equipment ("Handling Digital Photos: Heat Testing Part Two", June
2002). The test results indicated that thermal technology, as opposed to piezo
inkjet technology, was what allowed for the heat sensitivities when dry
mounting. And until recently my ISO scientists seemed to believe and agree with
my hypothesis.
During our most
recent ISO meeting, September 2005, I was challenged by the group that it is
not thermal vs. piezo inkjet technology but rather the paper coatings that may
actually be heat sensitive. So in October 2005 NielsenBainbridge agreed to
sponsor the fourth in my series of heat tolerance tests, this one to compare Epson
piezo inkjet technology, paper coatings, and inks under heat.
Heat Tolerance
Test #4 - Epson
Having used a
Hewlett-Packard 960c thermal inkjet printer as the control in my test I needed
to repeat the same basic test but this time using an Epson c86 piezo inkjet
printer. While researching printers I also discovered a line of Epson dye ink
printers, so my cover statement that all Epson printers are pigment is wrong.
The new heat
sensitivity hypothesis is that swellable coatings are more sensitive to dry
mount temperatures than porous ones. So in Test #4, I tested each 8x10"
image at multiple temperatures of 150̊F, 170̊F, 185̊F, 200̊F,
and 225̊F with a strip of vinyl laminate (photo 1). The results were way more revealing than originally
expected, as I was also able to identify differences in ink saturation, surface
durability and reaction to moisture.
Types of Paper
The biggest
challenge was going to be identifying the inkjet papers (photo 2). Inkjet papers may be uncoated, or coated with a surface
receptor. There are two types of coating: swellable and porous, plus either may
be applied to 100% paper base or resin-coated paper base.
Uncoated papers
contain a wide range of weights and surface textures. At one end of the uncoated
paper spectrum is 20# to 26# lightweight bond paper used as everyday printer
paper. The other end is mouldmade, fine art paper such as Arches, Rives BFK,
and Somerset. These may also come with different surface finishes including
rough, cold-press (CP) and hot press (HP), and most of these work with both
thermal and piezo printers using either dye or pigmented inks. Since inks
interact directly with the raw paper, uncoated papers soak up the ink rather
than being trapped by a coating, making colors generally less vivid and vibrant
(photo 3).
Uncoated papers
have two components: the base and the sizing. The substrate base constitutes
the weight, body, and surface texture of the paper as described above. The
sizing may have been added either internally during production or as a surface
sealer to control absorption of moisture, such as traditional watercolor
papers.
Coated papers may
be fine art or photo papers that have been treated with a receptor coating for
inkjet printing. The surface coatings may be of many different substances
including tiny glass beads, silica, clay, calcium carbonate, or assorted
polymers. They are designed to enhance and control the printed image and may
alter the base paper surface allowing for a variety of finishes from high gloss
to matte.
Coated papers are
classified by assorted designations and categories. They are fine art or photo
papers; the surface finish is gloss, semigloss, satin, or matte; and the by
coating is swellable or porous. These all help to indicate their intended end
use.
Swellable
(Polymeric, Non-porous)
Swellable coatings
are slow dry, moisture and humidity sensitive, relatively lightfast, and
resistant to gas fading. They are more photographic, glossy, and better geared
to dye based inks, though images may appear more grainy producing a more
noticeable dot pattern. Swellable coatings react differently to dye or pigment
and in turn colors may vary a great deal in final printed images (photo 4). When a drop of water is
placed on the surface it create a slippery film with the wet ink (photo 5).
Swellable coatings
are made of organic gelatin like polymers that surround and encapsulate the ink
when it hits the paper. The coating swells two to three times its original
thickness as it absorbs and spreads the applied ink. Once the coating has dried
it returns to its original thickness while encapsulating the ink droplets. This
is why it takes longer to dry once printed and is what makes them more
lightfast than porous coatings (diagram
1). Swellable media (papers) include: HP Premium Plus Colorfast Paper,
Epson Colorlife Photo Paper, and Ilford Classic Pearl and Gloss Paper.
Porous
(Microporous, Nanoporous)
Porous coatings
are fast drying, moisture resistant, more light sensitive and prone to gas
fading, but generally adapt well to printing of both dye and pigment inks. They
are more high resolution than swellable coatings, and are marketed as quick or
instant dry. When a drop of water is placed on the surface it is absorbed
resulting in no major change to the paper (photo
6). Excessive water may cockle the paper with no ink damage, while dye inks
may bleed or leave a ring.
Porous coatings
consist of tiny particles glued together with air spaces or 'pores' between
them. These pores suck the ink droplets into the open spaces as the water in
the ink evaporates (diagram 2). When
the ink dries out, an embedded layer of colorant remains in the coating.
Swellable coatings encapsulate the ink, while porous coatings spread the ink
out evenly over the entire surface within the coating. Porous media include: HP
Photo Paper, Epson Premium Glossy Photo Paper, Hahnemuhle Photo Rag, and
Crescent Digital Papers.
Microporous papers
differ from porous papers in that most have a receptor coating made up of
highly uniform ceramic (glass or silica) particles. They create a set of pores
that act as inkwells trapping the ink just below the coating surface. Inkwell
uniformity makes for quick ink absorption and drying, and unlike the clay
coated surface receptors they have better water resistance and less loss of
gloss after ink application. They work well for both dye and pigment inks and
most microporous papers also use an RC or polyethylene layer behind the coating
to eliminate waviness and wrinkles with heavy ink applications.
Resin-Coated (RC)
Resin-coated is
not really a coating at all, but rather a way in which the paper is
constructed. Similar to the standard RC papers familiar with traditional
photographs, the same concept is utilized in digital photos. It is basically a
paper substrate sandwiched between two layers of polyethylene, with either a
swellable or porous receptor coating applied to the top (Diagram 3). These papers
easily replicate the look and feel of traditional RC photos. Water droplets have a tendency to sit on the
coating surface until the air evaporates it, with no resulting change to the
paper once dry (photo 7).
Matching Inks To
Papers
There are two
basic categories for inkjet inks: dye and pigment. Dyes have a wider color
gamut and greater saturation, but are water soluble (photo 8). Papers designed specifically for dye printers include:
HP Premium Photo Paper and Ilford Galerie Classic Gloss. Pigment inks are more
light stable, are more insoluble in water, and there is a larger variety of
paper choices. Common pigment only papers include Ilford Galerie Smooth and
Epson papers. Most dye inks are paired with gloss or satin photographs, while
pigment inks are used with coated DFA papers. Then there are the coated DFA and
photo papers that will work with either dye or pigment inks including Crescent
Digital Papers, and Hahnemuhle Photo Rag.
Aside from
straight dye and pigment, there is also a third hybrid category of ink which
combine both dye and pigment. Examples of this are Epson's Ultrachrome Ink with
a lightfastness expectancy of 100-150 years when printed on designated paper,
and Epson Archival Pigmented Ink with a life expectancy of 200 years.
Tolerance Results
and Mounting
Though the results
of this Epson test on assorted swellable, porous, microporous, and resin coated
papers is somewhat inconclusive, all indicators point toward swellable photo
papers being heat sensitive at most dry mount temperatures, even as low as
F150. Swellable DFA papers, however, mount at all temperatures and even
tolerate laminating with no color shift.
The entire pigment
ink, paper, heat tolerance test will most likely turn into a full blown article
later this year, but for now be aware of mounting limitations with digital
photos. Most manufacturers do not list type of paper or coating on their
packaging, so if a photo is brought in for framing it is imperative you
establish brand, printer and ink. Requesting a blank or discarded image on the
same photo paper will easily determine a heat sensitive swellable paper by
adding a drop of water.
Understanding
digital papers is the key to protecting yourself when mounting, and the bottom
line remains...if you cannot determine the origin, cold mount or use
preservation techniques to be safe.
END
Photo 1 Epson
Heat Tolerance Test
Upper left top three
photos are uncoated DFA papers; top center eight are coated DFA papers;
upper right seven
are swellable; second row from bottom are porous; and bottom row are all
porous on resin
coated media. Each 8x10" photo has been divided into six strips and tested
for
heat tolerance at
F150, 170, 185, 200 and laminated at 225.
Photo 2 DFA
and Photo Papers
Inkjet papers may
be uncoated, or coated with a surface receptor.
There are two types
of coating: swellable and porous, plus either may be
applied to 100%
paper base or resin-coated paper base.
Photo 3 Swellable
Coated vs. Uncoated DFA
Left Jetprint
Premium Photo, a coated swellable paper. Right is Lanaquarelle HP,
and uncoated DFA
paper. Since inks interact directly with the raw paper, uncoated
papers soak up the
ink rather than being trapped by a coating, making colors
generally less
vivid and vibrant .
Photo 4 Color
Variations
Center top HP Glossy
Premium Photo Paper has a yellow tint; upper right Jetprint Premium Photo Paper
has a green tint;
lower right Ilford Galerie Classic Gloss is closest to the original photo
color; lower
left Epson
Colorlife Photo appears very green. All swellable, potentially heat sensitive
images.
Photo 5 Water
on Swellable Coating
When a drip of
water is placed on the surface , it does not absorb
and when rubbed it
creates a slippery film removing the ink from the coating.
Photo 6 Water
on Porous Coating
When a drop of
water is placed on the surface it is quickly absorbed resulting in minor
surface
change to the
paper, but papers may cockle. Though it looks like it is swelling it is merely
soaking in.
The water is
puddled on the paper but will dry flat.
Photo 7 Water
on Porous Resin Coated Paper
Water droplets on
coated RC paper will sit on the surface coating until the air
evaporates it with
no change to the paper once dry. Epson Premium Luster, porous, RC paper.
Photo 8 Water
on Microporous RC Paper
As in photo 7
water drop will evaporate rather than soaking into the coating,
but dyes are water
soluble and can run or bleed while
evaporating. This is also
what occurs when
using paper designed for pigment ink on a dye based printer.
Epson Glossy Photo
Paper, microporous for pigment on dye printer.
