Ordinary shellac is dark in color. Always use a bleached shellac solution when wood requires a light or ecru clear paint finish. The operation process of shellac bleaching is as follows:
Take bleaching 100 grams of shellac as an example, first add 500 grams of water and 8 grams of soda ash (Na2CO3) to the container and heat until dissolved, then add 100 grams of shellac, heat, stir continuously, and when it dissolves (the evaporated water must be continuously mixed). After adding), stop heating, move into another bleach container (pre-add the same amount of water as the shellac alkali solution), and slowly add (or add in several times) sodium hypochlorite solution (concentration is 10 degrees) under constant stirring Baume). At this time, the color of the shellac alkali solution gradually fades until the desired color is reached, add an equal amount of water, stir, and place it for 3o~6o minutes; filter, cool to 26~28c, slowly add 2o% dilute solution while stirring Sulfuric acid is neutralized, and the marked shellac precipitates out (the amount of sulfuric acid added is based on the complete precipitation of the shellac, and it is added until the solution is acidic, with a pH of 2~5). Then filter the solution, and wash the bleached shellac with boiling water several times until the residual acid and salt are washed away, then put it in hot water and knead it into the desired strip, and finally put it in cold water and store it in a dark place (The storage period is only 1~2 months, otherwise it will deteriorate and be insoluble). The bleached glue obtained in this way contains a certain amount of water and can be dried at low temperature (about 4°C) to make dry bleached shellac.
