The Painting Performance of Kosh Watercolor

Due to the improved standard of living , watercolor paintings are very popular in Taiwan . However, most of the famous Taiwanese watercolorists have used a lot of imported watercolor papers . Unfortunately , there is still lack of high-grade watercolor paper domestically made . The aim of this study which was sponsored by the Council of Agriculture intended to produce high-grade watercolor paper that might be comparable to Arches watercolor paper made in France since 1492 . The main characteristics of Kosh watercolor paper we made by hand on a laboratory scale were described as follows : * Density : 0.5-0.6 g/cm3 * Water absorbency : >28 g/m2(Cobb test) * Brightness : High brightness makes the color more brilliant . * Rough paper surface : Considerable luminosity and brilliance are created by the contrast between the reflective luster of the raised surface of a granular paper and the depth and richness of the heavily loaded color in the hollows. * Good color hold-out : Colored pigments should properly level on the paper surface. * Permanence : Alkaline sized and cotton-containing watercolor paper showed the greatest permanence. Comparing to the painting properties of Arches paper , Kosh paper showed some defects in the following respects : (i) White specks occurred on the painted paper surface after drying . (ii)Not easy to be painted in 2nd brushing (painting) . In order to solve these problems , we carried out this experiment "Improvement of the quality of Kosh watercolor paper " since 1995 . We proposed " Cobb testing method " to determine the color hold-out i.e., the tendency of painting color held or retained on the paper surface after paint drying , for all watercolor papers . The color ( expressed as CIELAB) and color difference of each test paper were determined according to respective TAPPI Methods , thus the coloring strength of each specimen can be ob Because of roughness affecting the painting properties of watercolor paper , Arches paper with lower roughness has an easy access of leveling the watercolor paint and no white specks presented on the painted paper surface compared with Kosh paper. Thus the white specks usually presented on the painted Kosh watercolor paper surface can be diminished by lowering its roughness . The experimental result of FTIR analysis revealed that gelatin which might present in Arches paper promoting the painting strength and picking resistance in the following paint brushing for watercolorists . In general , painting test results of Kosh paper indicated that a high-grade watercolor paper could be made domestically from appropriate formula i.e., cotton fiber, dry strength agent, alkaline size, CaCO3, painting aid, and surface size by handmaking technique .水彩畫作的表現，紙質所扮演的角色非常重要。一般畫家常以畫紙之空白 部分來表現亮度，紙面以天然白色最為理想。水彩紙需具適當之吸水性、 紙質結實、紙面粗糙度適中且富光澤、刷塗不起毛以及易於修改等特性， 而優良的顯色性更是不可或缺的必要條件。 為期客觀評估自製Kosh水彩紙之顯色性，吾人自創利用Cobb測試儀進行測 試水彩紙之顯色性。將此法著色之紙樣利用測色儀測定水彩紙著色部分之 顏色值，以CIELAB表示之。比較各種水彩紙之顏色值差異，即可客觀偵知 水彩紙之顯色性。又利用Cobb測試儀，將黃色水彩顏料覆蓋於藍色水彩顏 料之重疊顯色(綠色)法，可客觀地模擬水彩重疊上色之重疊顯色性。 自製Kosh水彩紙與法國Arches水彩紙之性質相較，Kosh水彩紙尚有著色後 之紙面有小白點及第二次上色不易之缺點，故繼續從事品質改良之工作。 由測定水彩紙表面粗糙度結果知，法國Arches水彩紙之較平滑表面相較 Kosh水彩紙易著色且不會有白斑出現 ; 故經改變Kosh水彩紙表面之粗糙 度即可消除上色水彩紙表面之白斑缺點。又利用FTIR技術對紙面進行組成 份性質分析及由文獻中知法國Arches水彩紙表面塗有動物膠，此種成分對 水彩紙之繪畫性及重疊顯色性均有甚大之助益。試驗至此，吾人可謂國人 已可自行生產高品質Kosh水彩紙矣