Chapter 3
Chemical Action for Making Printing Plate of LithographI will describe each detail of chemical action for making printing plate which involved in the primary materials except plywood:
3.1. Limestone Printing Plate
The limestone absorbs water well because the structure of the limestone is porous and the main component is calcium carbonate [CaCO3], more than 98%.
After having drawn an image on the surface of the limestone with the oil-based acid-resistant mediums, apply a weak acid solution of dissolving gum arabic in water and adding nitric acid [HNO3] onto the whole surface of the limestone.
The fat of oil-based drawing mediums is resolved by nitric acid, and fatty acid floats. This fatty acid saponifies with calcium carbonate and forms fatty acid calcium soap. Fatty acid calcium soap is not dissolved in water and turpentine. Lipophilic oxide layer is made on the surface of the image and it repels water and attracts fatty materials.
The surface of the blank space on the limestone is corroded a little bit by nitric acid and carbonic acid floats; this reaction saturates nitric acid with calcium carbonate gradually and forms calcium oxide [CaO].
Calcium oxide is hydrophilic and has the property of keeping water. This nature is still kept after washing gum arabic off the surface of the limestone: because this hydrophilic oxide film which is made of a calcium oxide already has been made on the surface of limestone by chemical action of nitric acid.
Fatty acid calcium soap on the part of the image attracts ink and the blank space repels ink by hydrophilic of calcium oxide and the porosity of limestone that is easily permeated with water.
Pure gum arabic solution without nitric acid has chemical action of making the hydrophilic oxide film and this solution is effective for the metal plate, but as for the limestone, the blank space would be easy of stain with ink.
3.2. Metal (Aluminum/Zinc) Printing Plate
It first needs grinding the surface of the metal plate coarsely for keeping water: because metal is not porous and this coarse surface makes that the plate takes the drawing mediums easily.
As for the aluminum plate, apply the brushing-up liquid on the surface of the plate before drawing image. This liquid makes the sensitivity higher for fat and acid.
The zinc plate is susceptible to oil and acid more than the aluminum plate, so it needs to take care not to put unnecessary oily. The lipophilicity of zinc is comparatively strong and the sensitivity is highly. This nature makes easily keeping a part of image and the durability of the image is good in printing. Though, it is the weak point in the zinc plate that the blank space is easily made dirty and the part of image is gotten fat. A speckled pattern is the features tone peculiar to the zinc plate compared with the aluminum plate.
After having drawn an image on the surface of the metal plate with the oil-based acid-resistant mediums, apply a weak acid solution of gum arabic in water: add phosphoric acid [H3PO4] for aluminum and the pH of the weak acid solution is better between 2.0 and 3.0. Pure gum arabic solution without phosphoric acid has chemical action of making the hydrophilic oxide film and this solution is effective for the metal plate, but it takes time.
The fat of oil-based drawing mediums is resolved by arabic acid, and fatty acid floats. It is lipophilic but still unstable and weak, so it needs replacing fatty acid with the lacquer. It is possible to use the silicon instead of the lacquer: it is cheap and easy parts the ink.
It is said that fatty acid is not saponified to make fatty acid calcium soap because metal is not alkaline. However, I suppose about some possibility to saponify by alkalinity of the talcum powder at first etch, and or fatty-acid metal salts (metal salts of fatty acids) is saponified.
The hydrophilic film is formed on the surface of the blank space by arabic acid: aluminum oxide [AlPO4] is on the aluminum plate and zinc oxide [ZnO] is on the zinc plate, respectively.
Lithographic Etching: It is a unique technique to get some peculiar line and pattern by corrosion with the zinc plate.
After corrode the zinc plate with dilute nitric acid [HNO3] or ferric chloride solution [FeCl3] same as intaglio, apply lacquer on the whole surface of the plate and scrape unnecessary lacquer off. Apply a weak acid solution of gum arabic in the water on the surface of the plate for making printing plate and print as a planograph.
I tried to do it with the aluminum plate. Aluminum plate is very thin but it is enough for corroding shallow.
This technique has both characteristics of the planograph and the intaglio printing. Also the plywoodgraph has both characteristics of the planograph and the xylograph. I would like to develop new unique technique like them because the advantage of planography is the high liberty.
3.3. Polyester/Frosted Glass Printing Plate
Each technique is called polyester lithography and frosted glass lithography. The basic principle is the same as common lithography; however, in this technique, it does not give chemical reaction on the surface of the printing plate and it is the difference between this technique and common lithography.
It first needs grinding the surface of the polyester and glass plate coarsely for keeping water as well as metal plate: because polyester and glass are not porous and it makes that the plate takes the drawing mediums easily.
The processes for making printing plate is just only apply a weak acid solution of gum arabic in water after having drawn an image on the surface of the polyester or the glass with the oil-based acid-resistant mediums.
Absolute alcohol is used for removing the image, and or it is better to use both absolute alcohol and toothpaste. It would influence for the capacity of keeping water to scrape the image off the surface by scraper and sandpaper.
This technique had been newly developed to omit complex processes of the planography for kids first but there are some artists who produce their works with this technique at present.
Thus, new technique like this helps artists and extends their field of activity: it is easy and convenient also for them especially in case they cannot have enough facilities. Also the way like this will be able to help students greatly when they finished school and are fledgling artists.