Sabina Bračko

In the complex process of recalling a distinct colour, memory plays a crucial role. The accuracy of recall is particularly important in some cases, for example when recognising the colour of food, as it communicates information about its freshness, taste and ripeness. Food manufacturers establish their first contact with consumers through various forms of advertising. To attract attention and encourage purchase, the colour of food must be carefully selected and depicted. This process relies on memory colours for different groups of fruit and vegetables, i.e. the colours of well-known and frequently seen objects. In 2024, a new Preferred Memory Colour (PMC) chart was published, which contains the memory colours of selected objects and foods and enables accurate colour reproduction. The purpose of the present research was to investigate the influence of the mode of colour presentation on the observer's ability to recall a colour sample, namely the colour of fruit or vegetables. In the experiment, three different ways of presenting the colour were used. The experiment took place in a controlled environment under constant observation conditions. The colour vision of the observers was previously checked with the Farnsworth-Munsell 100 Hue test. The test charts were prepared based on the preferred colours of selected foods, and the results were numerically evaluated using the parameters of the CIELAB colour space. The results showed that the accuracy of colour recall is greatly improved with additional directed instruction, due to subconscious associations with a specific object. In addition, it emerged that some food colours are remembered more accurately than others.

The durability of the materials is often limited as they fade under the influence of external factors, particularly light. The present research aimed to study the photodegradation of commercial inkjet inks in an aqueous solution. The results were compared with their stability on prints in order to establish the connection between the kinetics of photodegradation of dye in the solution and the durability of the final print. Thin-layer chromatography (TLC), chromatography with a mass selective detector (GC/MS), and spectrophotometric measurements were used to study the effect of light, including near UV. The results clearly show that the catalytic effect between different dyes cannot be avoided, as the inks for inkjet printing are usually a mixture of different colorants. A comparison of the results of photodegradation of the dye in solution and on the final prints does not show a direct connection due to the different influences of external factors. Consequently, it was established that it is not possible to predict the photodegradation of prints solely based on a single dye’s analysis in solution. The paper as a substrate must be included in the analysis, as it significantly influences the photodegradation of the print.

When studying the process of photodegradation, we often deal with the durability of the individual ink colour components, the durability of the printing material or the durability of the ink on the printing material. Less frequently, ink degradation in the solution is compared to the print. However, it is essential to consider all the crucial external and internal factors that influence the photodegradation process in the context of the durability of printed materials. When studying photodegradation, external factors such as light, temperature and humidity are relatively easy to control. On the other hand, the control of internal factors in the photodegradation process is much more complex since the internal factors are related to the composition of the ink used, the substrate and the physical and chemical processes between them. The study aims to analyse the complex degradation process of prints made with an ink-jet printer compared to the degradation of the same inks in an aqueous solution. The study included two types of paper and an ink-jet printer using dye-based inks. A high-pressure mercury lamp was used to irradiate and accelerate the degradation process, and a specially adapted reactor was used to irradiate solutions and prints. The results showed how short-wave UV radiation significantly influences the changes of the printing material, ink and prints. In some cases, the difference between the ink stability in solution and ink stability on the printing material can be observed. The effect of paper on the durability of the print is, however, negligible in the case of short-wave UV radiation. The process of photodegradation of the paper under UV radiation was mainly manifested by the loss of specific surface and optical properties.

Photodegradation of the ink‐jet prints is a complex process in which many external and internal factors are involved. Nevertheless, the role of colorants and various accompanying substances in the ink is often overlooked. Our research work aimed to determine the fastness of water‐based ink‐jet inks in aqueous solutions. A printing ink often contains a complex mixture of colorants to achieve optimal optical properties of color and a suitable fastness of the print. Therefore, we investigated the composition and stability of cyan, magenta, yellow, and black inks under the influence of UVC light in the presence of oxygen as well as in an inert environment based on TLC chromatography and spectrophotometric analysis. The process of photodegradation was evaluated based on ink amount and half‐life. According to the results, the majority of inks consist of at least two colorants that differ in color and polarity. The results have shown that the presence of oxygen negatively affects the stability of inks; therefore, the inert atmosphere prolongs the durability of ink in water solution.

Three frequently used formulas and their power function modifications were used to calculate the colour differences after the exposure to light and to study the stability of ink jet prints by spectrophotometric measurements. The prints...