It is evident that Hanji and ink stick are essential materials to the conservation of paper cultural properties, which calls for active research efforts on traditional ink sticks and Hanji used in old cultural properties and on modern ink sticks and conventional Hanji used today. However, there is no study on the effects of different types of ink stick, which include modern Chinese ink in the market and traditional ink stick made from pine-burnt soot or oil-burnt soot, on the heat treatment of Hanji. There are only a couple of studies on the patterns of heat treatment in ink stick-applied Hanji.
This study thus set out to investigate the heat treatment characteristics of Hanji according to the types of ink stick used in books and Oriental paintings. Total two types of materials were selected for the study; conventional and traditional Hanji was treated with glue and turned into glue-up conventional and traditional Hanji. Total four types of Hanji were used in the study as materials. Two types of traditional ink stick and one type of ink stick on the market were applied to the four types of Hanji to make samples. The ink stick-applied samples were put to artificial heat treatment under artificial moist heat treatment conditions for 15 and 30 days and to accelerated aging treatment under light aging treatment conditions for 24, 48, and 72 hours. They were then examined for basic properties, optical features, folding endurance, zero-span tensile strength, and surface analysis with an optical microscope. Following SEM and SEM-EDS analysis, comparison and analysis were performed according to the types of ink stick, accelerated aging treatment conditions, and heat treatment.
The Hanji samples were measured for such basic properties as weight and thickness. The weight measurements indicate that no glue-up treatment resulted in a higher increasing rate of weight after ink stick application than glue-up treatment and that glue-up treatment resulted in a greater decreasing rate of weight after artificial heat treatment than no glue-up treatment.
The analysis results of Hanji''s optical features show that there were greater color changes in artificial moist heat treatment than in light aging treatment. Glue-up conventional Hanji especially displayed very huge color changes with the ΔΕ value at 15.45 after 30 days of heat treatment. The ink stick-applied samples, however, exhibited little color change with all the three types of ink stick showing little color change according to artificial heat treatment.
As for folding endurance, artificial moist heat treatment led to a greater decreasing rate than light aging treatment. Glue-up samples showed a greater decreasing rate of folding endurance than non-glue-up samples, presenting poor heat treatment stability. Glue-up conventional Hanji, in particular, recorded more than 99% of decreasing rate in folding endurance 30 days after artificial moist heat treatment. Zero-span tensile strength showed no great decreasing rate unlike folding endurance, whose decreasing rate was enormous.
Comparison and analysis were performed on the ink stick-applied samples before and after artificial heat treatment with an optical microscope. As a result, there were alum particles added to the glue solution found between fabrics in the glue-up conventional and traditional Hanji, and they would decrease in size or disappear after artificial heat treatment. The ink stick applied to fabrics was partially changed in color after artificial heat treatment.
The SEM and SEM-EDS analysis results reveal the deterioration of heat treatment stability in the sample surfaces after heat treatment with openings increasing and cracks happening in fabrics. Surface changes were especially great in the glue-up samples, whose heat treatment stability turned out to be poor. While the main components of ink stick-applied Hanji were C and O, traces of Al and S were detected in glue-up Hanji.