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| PDF : |  11020041.pdf |
| title(En) : | Studies on the Discoloration of Wood III. Acid Stain |
| author(En) : | Katsumi Takenami |
| information : | Mokuzai Gakkaishi 11(2), 41-46 (1965) |
| assort : | Original Article |
| summary(En) : | Acid stain is a trouble frequently found in decorative plywood manufacture. In this paper, studies were carried out on (1) the relation between pH and acid stain with oxalic as well as hydrochloric acid, (2) influences of light and (3) stain-sensibility of 19 different woods. Specimens of sliced veneer soaked in acid solutions of various pH were exposed to light in different ways such as under mercury lamp, indirect sunlight in experimental room, or put in a dark place. Color difference (NBS unit) of the treated specimens were were measured by HUNTER color and color difference meter; furthermore, spectral reflectances of 19 different woods were measured by spectrophotometer to calculate their trichromatic coefficients. Results obtained are as follows: 1) In acid stain, color development is, first, rather strong, but gradually fades away presumably due to photochemical reaction (Fig. 1). As coloration is almost the same in nitrogen atmosphere as in air, it appears that oxidation by air does not have a direct relation with acid stain (Table 1). 2) Acid stain remarkably increases below pH 1.5∼2 but is very weak at pH 2∼5 as seen in Fig. 3. 3) Colorations were all pale red, similar to each other, and could be divided into three groups: strong, medium, and weak, as shown in Table 2 by visual inspection. From figures given in the table, any relation between acid stain and tannin content could not be found. 4) Specimens extracted with hot water did not give coloration with acid. This fact would lead to the conclusion that extractives like polyphenols and related substances are responsible for the acid stain. |