In order to characterize the image for fade due to light, it can be exposed to a very high intensity light source, with the following conversion of the exposure to real time. A care must be taken to match the spectrum of the expected light exposure to that of the light source used in accelerated test. Thus, the fraction of ultraviolet component in the light source must be carefully adjusted.
When the test is designed to simulate the exposure to sunlight (either direct, or filtered through the window glass), it is common to use Xenon Arc light source with appropriate UV filters. In a fade machine, the samples are mounted in a lantern arrangement around the central Xe-Arc source, and then constantly rotated to equalize the exposure.
Alternatively, the samples can be exposed to light real-time in areas where the sun exposure is very high. If appropriate controls are put in test, relative performance of different systems can be compared this way.
This is something that worried people for a long time. For how long will the information last- and if it will decay, how? We have some wonderful examples of a long preservation. We will not talk about cave wall art (which is perhaps 45,000 years old) and information written in stone, such as Rosetta Stone (196 BC). The oldest way to write something that would resemble books was on three Ps: Papyrus, Parchment and Paper. Papyrus is the oldest media known to men. The oldest papyrus that was dated is about 4500 old and the text is still readable. The Yuya Papyrus shown in this website, made in beautiful color is dated at 1390 BC. Fast forward and Dead Sea Scrolls found in 1950s, are as old as 300 BC, were written partially on parchment and partially on papyrus; the content of biblical texts is still readable and authentic, according to the scholars.
Paper as we know it was invented in China and the oldest paper document (a map) is dated 179 CE.
Whenever documents degrade, it is rarely due to the fade of inks. Most commonly, the media itself degrades due to rot or to fire.
This is something that we may be facing soon or perhaps are already facing. How long will the information recorded in digital format will remain readable? The danger is not only the degradation of the digital data carriers, but the progress in technology that makes the old data carriers obsolete. Some of us perhaps are facing this already as we cannot access our old floppy disks the new computers do not have floppy drives. The CDs and DVDs are still accessible but perhaps not much longer. The data can be stored on a cloud of course, but the cloud companies can go out of business. I am wondering if the digital information that has been generated during the last 20 years will still be accessible in 100 years from now.
One of the main challenges is to have a textile colorant bound to the textile. After the coloration is complete, the colorant must withstand washing cycles, and, when exposed outdoors, be stable to weather elements such as rain and sun. This is particularly challenging as the colorants are often applied as a solution/dispersion in water! Many technologies have been invented to convert the dye from soluble to insoluble form. For example, one can make the dye water soluble at higher temperatures, apply it to a textile and then have it made bound/insoluble in water at lower temperatures, at which the garments are used (or washed). These sparingly water-soluble dyes are called disperse dyes. Alternatively, one can rely on a partial conversion of the dye/pigment into an acid form to react with amino groups (in, e.g. Nylon) on the contact with textile (acid dyes) . Yet another option is to convert a water-insoluble dye into a water soluble form in a basic solution, with the following oxidation step to convert it back to water-insoluble form (vat dyes). Does it have to be so complicated? Direct dyes on the other hand can have enough affinity to textile by itself, without the stages pre-and post-treatment; however their waterfastness tends to be poor. Many textile dye chemistries are now available and are catalogued in Colour Index, first published in 1924. In the old times, dye chemical structures were heavily guarded by the manufacturers and the Colour Index database served as an intermediary between the dye manufacturers and the textile colorists. This produced many cryptic dye names (e.g. Acid Red 52) that do not disclose the dye structure. While it is still true for some dyes and pigments, many structures are now in public domain and can be found in monographs or on internet.
The textiles can be colored monochrome (single color) at the stage of the fiber manufacturing or immediately after; this process is known as dyeing, as opposed to textile printing, when the parts can be made in multiple colors by using more advanced printing methods such as screen printing. Inkjet recently has become available as one of the methods of direct printing on textile.
Pigments in India, on market stall
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Dye sublimation is the process of conversion of a dye from solid state to vapor on contact with printing media. Often, the pressure is also applied to facilitate the transfer. The Cyan-Magenta-Yellow colorants can be incorporated into a polymeric film and diffuse into the printing media on the contact with a digital heating element. As the dye becomes vaporized, it becomes fully integrated with the substrate, on a molecular level, which makes dye sublimation prints very durable; also the colors become brighter as the dye/pigment de-aggregates. As the dyes for the sublimation process need to be easily vaporizable, this limits the colorant structures to lower-molecular weight, apolar chemistries.
It now becomes more popular, with the applications such as custom apparel items, e.g., for sports events, soft signage, flags, etc. The area is highly dynamic and new technologies are constantly developed. A nice review has been recently given elsewhere. One can print direct on garments with disperse, acid and reactive dyes. The downside of this technology is the incomplete binding of the dyes and multiple washing cycles may be required to remove unbound dyes. Alternatively, one can print using color pigments. Those will reside on the surface of a textile and generally can also be washed away and rubbed off, however it can be not an issue if the application does not involve a physical contact (e.g., signage). Finally, one can print he dye sublimation dyes on an intermediate substrate, with the following transfer on a textile under pressure and high temperature. As a result, very bright colors will be produced as the dye sub dyes de-aggregate and penetrate into the fibers.
