Printing colors on glass & porcelain: a matter of experience
If one of our printed mugs bears your corporate design, the reproduction of your company colors should be as accurate as possible. We explain what the result has to do with experience - and under what circumstances it is possible to achieve almost 100% color fidelity.
Now that's it! Your promotional mug, porcelain mug, enamel mug or glass with an individual imprint from Granvogl. The imprint of your logo looks exactly as you imagined it would, and the quality of the porcelain or glass is just right anyway. You are completely satisfied ... only: If you hold one of your business cards next to it, the logo color on the cup differs slightly from the original.
This is a phenomenon that cannot be prevented depending on the printing process - despite all the care we take with our hand-applied printing. The reasons are of a physical or chemical nature and can never be completely avoided. However, any color differences can be reduced to a minimum thanks to the experience of our printers. The printing process itself also plays a role - our new low-temperature process, for example, reduces deviations to an absolute minimum. By way of explanation, allow us to take a brief, informative excursion into the world of color:
CMYK? RGB? Pantone©? HKS©? What is all that?
You have probably already noticed that your website looks slightly different from your brochure - the colors are slightly “shifted” and the print on paper looks a little paler than the image on the monitor. Although this is not necessarily desirable, it is actually quite normal. Because, to put it simply and without getting too technical: On the monitor (RGB color space), all colors are represented by red, green and blue, whereby each color can take on 256 different gradations. In print (CMYK color model), on the other hand, four colors, namely cyan, yellow, magenta and black, are used in tiny printing dots, the halftone screen - each in 100 possible gradations. In addition, the screen colors shine “on their own”, while paper reflects the incident light. And as if the differences weren't big enough, the way the monitor is calibrated and the color temperature at which the light falls on the paper also play a role.
Standardized colour systems have been developed to ensure uniform colors, at least in printing - Pantone© and HKS© are well-known examples that we work with. These colors are also called spot colors.
Such color systems are preferred when designing logos and defining corporate colors: They are standardized and there is a defined color fan for each color system, which means that all parties know exactly which color they are talking about.
How can maximum color accuracy be achieved?
First of all, even if you have selected exact specifications for your corporate colors as part of your corporate identity, the print results will always differ slightly. Depending on the substrate (e.g. paper, fabric, ceramic) and the inks used. At Granvogl, for example, we use ceramic inks for high-temperature printing, while organic inks are used for low-temperature printing. Generally speaking, printing with organic inks enables more precise color reproduction, while printing with ceramic inks and subsequent firing at high temperatures is more resistant. Granvogl offers both processes - depending on the customer's requirements, whether almost 100% color accuracy or higher resistance is crucial.
Printing and high-temperature firing
Ceramic paints are used here. These consist of various metal oxides, which are mixed into colors in the form of powders. Each Pantone© or HKS© value must be mixed separately from several components.
After printing, the motifs are fired in our kilns at 640°C or 850°C. This melts the surface of the porcelain. The surface of the porcelain/glass melts, the color sinks in and the surface is sealed again when it cools down. In a sense, the print is not on the item, but in the material.
During this process, with its extremely high temperatures, the ceramic color changes within a certain range, and the result can deviate from the originally desired color. Every metal oxide behaves a little differently here.
This is where the experience of our screen printers, who are true craftsmen, comes into play: After many thousands of firing processes with a wide variety of colors, they are very good at estimating the direction in which a color will change as a result of the firing process. When mixing a solid clay from ceramic color powder, they already take this into account and mix the desired color with the corresponding deviation, which is then “corrected” in the kiln.
If a very accurate color reproduction is required for orders, we strongly recommend that you produce a proof sample: the desired imprint is first transferred to one of the items you have ordered as a single piece and fired. You will then receive this sample for checking and approval. Only when you are satisfied will we start printing the entire print run.
Printing and low-temperature firing
The inks used here consist of organic material that hardens at “only” 200° C. This means that this process is also suitable for printing on materials that cannot withstand such high temperatures, as is the case with ceramics or glass.
By avoiding high temperatures, there is no change in the color particles, but also no fusing with the porcelain / glass. The cured colors are therefore closer to the specification, but the print is not completely scratch-resistant. However, the prints are suitable for the dishwasher and meet the requirements for a durable print suitable for everyday use in the colors you expect.
This is also the great advantage of low-temperature firing: the color options are practically identical to screen printing on paper. In contrast to ceramic inks, “critical” tones such as pure magenta or cyan can also be implemented. Even light shades and motifs on darker porcelain are possible and offer impressive color brilliance thanks to underprinting in white.
Nevertheless, a proof sample is also recommended here: This not only allows you to see the high color fidelity for yourself, but also to check whether the robustness of the print meets your specifications.
Who decides on the color quality of a printed mug from Granvogl?
When printing with low-temperature firing, the result after firing and curing does not deviate from the original motif print. With high-temperature firing of ceramic inks, however, the following applies: For orders without a proof sample, we print and fire the entire print run in a single pass. We can then only see for ourselves after firing how exactly the desired shade has been achieved. Our quality check then determines whether the deviating shades are still within tolerance and we can deliver the print run or whether we need to make further improvements..
However, we can limit this risk very well thanks to our decades of experience. This is because our printers produce so-called color plates after they have created a new full-tone color value with ceramic colors. These are ceramic samples that are printed with the color and then fired in the kiln. This makes it possible to determine very precisely how the color behaves during firing and the color recipe can be adjusted accordingly. All plates are archived and provided with the corresponding color recipe.
In this way, Granvogl has built up an extensive archive of color samples over many years, thanks to which we can reprint colors as accurately as possible.
Once again, we would like to point out that if a very precise color reproduction is required for orders, we recommend that you produce a proof sample. The desired imprint is first transferred to one of the mugs you have ordered and fired. You will then receive this sample for checking and approval. Only when you are satisfied will we start printing the entire print run.
