Lesson 3: Inks & Varnishes
Taught by Professor Timothy Cann
Okay, class, today we're going to address printing, one of the most important stages of custom tin design. Over the next three classes we'll be covering some of the technical processes involved, such as four color process and offset metal lithography, but for today we're just going to discuss the types of inks, coatings and varnishes used, and what applications they serve. Almost every tin is printed, even if it's just a varnish. So pay attention, because this will undoubtedly be a significant part of your exam.
There are three basic stages of printing in tin manufacturing. These are commonly known as coating, printing and varnishing. Not every tin will require every stage, but most go through all three, layering different inks and varnishes for different effects.
3.1 - A tin with an interior pigmented coat
The first stage is coating. A coating is applied by a coater, which, unlike an offset printing press, covers an entire sheet of metal rather than a select area. Coatings are liquid mixtures that can vary greatly depending on the desired purpose. Printing will usually start with a transparent size coating, which acts much like paint primer, increasing adhesion between the metal and the inks used later in the printing process. Pigmented coatings can be employed to create a tin that is one uniform color, to lacquer a tin with a gold or other metallic finish (fig. 3.2), or to lay down a white background to intensify the color of subsequent prints. Frequently, coatings are also used on the interiors of tins as in figure 3.1, above, either for cosmetic appearances or as specialized coatings employed to prevent acidic or water-based products from interacting with the metal.
3.2 - Partially obscured by subsequent prints, a gold lacquer undercoat is integrated into the tin's design
The second stage is printing. Unlike a coat, a print selectively applies ink only to certain areas of the tin surface to create a design by use of a process called offset metal lithography, which we'll explore in the third lesson on printing. Since inks and coatings are applied by different techniques, they differ greatly in composition, most obviously in that inks are considerably more viscous, resembling toothpaste more than the liquid coatings. Since only one color can be printed at a time, most tins will undergo multiple prints to create designs with varying colors (fig. 3.3, right). Inks can be mixed to match colors, including PMS and other international color standards.
3.3 - This design required a separate print for each color... black, white, red and gold.
If a large number of colors are required to achieve the desired look, such as for a photo image, four color process can be employed to create any color with only four prints. We'll explore four color process more thoroughly in our next class. Also, different types of inks can be used to varying effects, such as employing transparent inks to create an iridescent look (fig. 3.4, right).
3.4 - Transparent inks create an iridescent look
Varnishing is the last stage. Varnishes are special types of coatings applied at the end of the printing process, primarily to provide a protective layer to inhibit rusting and make the printing more durable. However, special varnishes can serve a number of design purposes. Their opacity can be adjusted to create different gloss factors, from a flat matte to a high gloss. Also, textured varnishes can be employed to drastically change the look or even the tactile quality of a tin, as with a crackle varnish (fig. 3.5, left) or leather varnish. One type of varnish that isn't easily categorized is a printable varnish. Printable varnishes are applied at the end of the process like other varnishes, but are more like highly specialized clear inks that can be applied selectively using offset lithography. As a result, for example, you can have a tin that employs both gloss and matte varnishes as a design element.
3.5 - A textured varnish, such as this crackle varnish, can create an unusual look and feel to the touch.
That's part one of our printing lesson, folks. We'll continue next with more detail on four color process, and then finish up the printing segment with a lesson on offset metal lithography. Don't forget to pick up last week's papers on the way out!