Glass Transfer = Ceramic
Decal
Printed transfers have been utilized for decades to make detailed
images that are permanently applied to an almost limitless range of
ceramic and glass products: drinking glasses, collector plates,
bottles, jewelry, appliance components, sanitary ware, table
settings, tile, cookware, pottery, and much more.
The terms "transfer" and "decal" are used interchangeably,
representing the image that is printed separately and then removed
from its backing paper to be applied to the final product. This
unique manufacturing process uses special pigments called ceramic
oxides that, when fired in a kiln, permanently bond with the
substrate (base item).
Confused?
Jump down to our
glossary to clear up any new terminology!
It is important to note that ceramic decals are the name for
printed transfers manufactured for a variety of substrates,
including glass. They are called ceramic decals because of the
pigments used, ceramic oxides. The major difference is that glass
products must be fired at lower kiln temperatures and, therefore,
decals for use on glass are built with specific pigments that will
fuse properly in the lower temperature range. Any reputable
manufacturer will tell you the ideal temperature at which their
decals should be fired; custom manufacturers will work with you to
make sure the range is appropriate to the product you are
decorating.
Building a Transfer
Ceramic decals are created by screen printing onto a special paper.
The paper is coated with either a water-soluble gum or a thin wax
so the image can be separated from the paper after printing. The
decal is held together and protected by a special top layer called
the covercoat, which burns off during firing.
The pigments used in a transfer are selected specifically for the
substrate to which it will be applied. Factors including the
maximum firing temperature the item can bear and how it will be
used by the consumer are especially important in creating a durable
and saleable product. Glass generally fires several hundred degrees
lower than similar ceramic items because the ceramic temperature is
too hot for the glass - it would melt. Because the ceramic oxides
require a certain temperature to properly bond to the substrate, a
glass piece could not use a decal manufactured to fire at
1450° F.
The intended use of the product is important to both make sure the
item will withstand regular wear, such as dish washing, plus ensure
it meets all legal criteria. There are a number of federal and
individual state regulations concerning lead (Pb) and other toxic
heavy metals traditionally used in ceramic decorating. These metals
are used to create bright and durable colors, although technology
in heavy metal-free decorating has come a long way and is available
from quality decal printers. More information about toxic heavy
metal regulations can be found at
unleadeddecal.com
Once the basic criteria are established, the pigments required to
print the specific image are mixed and milled to create a smooth,
consistent ink. The screen printing process uses one color at a
time, layering them with a drying period in between each color. A
decal can consist of only one to ten or more layers of color,
precious metals, or conductive paste. After all layers of the
design have been printed, the covercoat is applied with a final
printing pass.
The expertise involved in ink formulation, printing detail, and
final inspection make this manufacturing process as much of an art
as it is a science. No two manufacturers (printers) operate with
the exact same processes or quality standards.
Applications
Transfers offer several advantages over other methods of decorating
glass. First and foremost, a transfer is printed on a flat sheet of
paper instead of directly onto curved or irregular surfaces,
resulting in superior accuracy and consistency from piece to piece.
For similar reasons, decals are versatile in allowing detailed
four-color process, tight registration, and various special effects
like raised print or incorporating precious metals into a design.
During decoration, significantly less set-up and clean-up time is
needed for applying decals as opposed to a direct-screening process
and decals are excellent for just-in-time production or
interruptable processes.
While ceramic transfers offer many benefits, they cannot be the
best decorating method for every project. The development work and
fixed cost materials required for screen printing make
small-quantity custom work less cost effective. Decals generally
become economical with a minimum of one hundred printed sheets,
which may equate to hundreds or even thousands of pieces depending
on the size of the design.
Another consideration is the application process and time frame.
The most common format of decals is for waterslide application, in
which the base paper is coated with a gum that dissolves in water.
After a brief soak, the decal is slid off the paper, directly onto
the substrate (see photo below). A squeegee or lint-free cloth is
used to make sure no excess water or air is trapped under the
decal. It is recommended that waterslide decals be allowed to dry
overnight before firing.
Another method, which is much faster because it is automated with a
machine and requires no drying time, is heat release application.
Decal paper for heat transfer comes in large rolls with a wax base
that will melt and allow the transfer to adhere to its substrate.
These are best suited to large industrial operations with
consistently high volumes that can support the investment and space
required for a heat transfer machine.
How to Purchase Transfers
Ceramic decals can be found most easily and in the greatest
selection on the Internet. Some companies produce both a stock line
of standard designs that can be bought in small quantities in
addition to custom printing services where you provide the design
and specifications. Some companies are focused on only stock or
only custom manufacturing. A search for "ceramic decal
manufacturer" should bring you a good listing of options.
Quality decal manufacturers will engineer the decal to work best
with your specific substrate, firing environment, and other unique
characteristics of your product. The bonding of a ceramic decal to
its substrate is a chemical reaction that is most effective when
all important variables have been taken into account.
Always be sure the firing range for the decals you purchase is
within the temperature your ware, and your kiln, can handle. It's
also important to remember that ceramic oxides can fire into
different, generally brighter colors than you see on the pre-fired
decal. If you have a fired sample of the decal or a quality image
of how it will look once fired, base your purchase decision on the
fired appearance rather than the covercoated, un-fired decal.
Custom Decal
Manufacturing
In order to reproduce artwork or a specific type of image, a custom
ceramic decal is necessary. You will need a high quality graphic
(300 dpi/ppi at actual size) or at least an idea of the image you
want and your budget for purchasing or licensing a copyright, or
having it designed for you.
You may need to send a sample of the image (a lower-resolution web
graphic or PDF, or a hard copy) prior to beginning custom work for
a complete and accurate price quote. Depending on the design, there
could be a number of printing screens required and/or special
degrees of difficulty in reproducing the effects desired for your
glass or ceramic piece. Ideally, you should also have a physical
sample of the piece to be decorated; the manufacturer will use it
for fitting purposes and may do a test-firing if you have a proof
decal run. When you discuss your needs with the manufacturer, all
of these details can be worked out prior to beginning the
project.
The fixed costs of custom printing mean that the per-piece cost of
a ceramic decal will decrease as your quantity gets higher. No
matter how many decals you need, the printer will need to perform
the same graphic manipulations, ink formulations, screen making,
press set-up, and press clean-up. All these things must happen
regardless of the quantity.
Glossary of Industry
Terms
ceramic decal - a printed image used for permanent glass
or ceramic decoration that is transferred from its base paper and
applied and fired onto a substrate
ceramic oxide - an inorganic pigment that permanently
bonds with ceramic and glass substrates when properly mixed in an
ink formulation and fired in a kiln
ceramic transfer - another term for ceramic decal
covercoat - a layer of organic material that encapsulates
the color and burns away during firing
firing - the process of heating a ceramic or glass item in
a kiln at high temperatures. This melts the ceramic oxides in a
decal and permanently bonds them to the substrate.
four-color process - printing system using four base
colors (cyan, magenta, yellow, black) to produce a gamut of
colors
gamut - a complete range of colors created by a set of
like pigments
glass decal - another term for a ceramic decal
specifically manufactured to fire onto a glass substrate
glass transfer - another term for a ceramic decal
specifically manufactured to fire onto a glass substrate
heat release - decal application method requiring a heat
application machine. Decals for heat release are printed on a
wax-coated paper; the machine melts the wax and transfers the decal
directly onto the substrate.
ink formulation - the mixture of pigments and a liquid
base used to print a specific color
inorganic - a type of pigment, such as a ceramic oxide,
that will melt and fuse to the substrate during firing
kiln - special oven used for firing glass and ceramics at
high temperatures. Kilns are available in a range of sizes, loading
formats, and firing capabilities.
palette - a range or group of colors with similar chemical
composition
pigment - the base coloring substance, for decals a
ceramic oxide, used to create the ink for printing a color
screen - a grid of fine wire stretched across a frame
through which ink is pressed to reproduce an image
spot color - also referred to as "picked color," a
specifically formulated ink printed alone or as a supplement to
other layers. May be used to enhance four-color process.
substrate - the glass or ceramic base item to which a
decal is applied and fused during the firing process
waterslide - decal application method in which the paper
is soaked briefly in water, dissolving the gum coating and allowing
the decal to be transferred by hand onto the substrate
About the Glass Transfer web
site
Heinrich Ceramic Decal, Inc., a custom manufacturer of high quality
transfers, created this site to serve as an informational resource
on the use of ceramic decals in glass decorating. Heinrich has over
29 years of experience engineering custom decals for a wide range
of product specifications. You can contact Heinrich by calling
1-508-797-4800, e-mailing
info@heinrich.com, or visiting their web site:
www.heinrich-decal.com
© Copyright 2005 Heinrich Ceramic Decal, Inc. All Rights
Reserved.
