Adhesional wetting on zinc plate is usually measured by contact angles. Contact angles of water, linseed oil varnish and lithographic ink on zinc plate which was treated with various surface-finishing agents were measured in this experiment.
At first, means of pre-finish on zinc plate were tested with the following agents.
1. Liquid neutral detergent
2. Cleanser
3. 1.5% NaOH, 10% Na₂CO₃
4. 1.5% NaOH, 10% Na₂CO₃, 5% HNO₃
5. Ho-zumi (Special charcoal)
The result of various pre-finishes (Fig. 6-14), Shows that the method of polishing the plate with Ho-zumi for 12 minutes was best.
Zinc plate which had been thus pre-finished was treated with following counter-etching solutions.
1. HNO₃-K₂SO₄⋅Al₂(SO₄)₃ (A)
2. HNO₃-K₂SO₄⋅Al₂(SO₄)₃ (B)
3. HNO₃-K₂SO₄⋅Cr₂(SO₄)₃
4. K₂SO₄⋅Al₂(SO₄)₃
5. Al₂(SO₄)₃
6. K₂SO₄
7. K₂SO₄⋅Cr₂(SO₄)₃
8. Cr₂(SO₄)₃
9. HNO₃
10. H₂SO₄
11. HCl
12. CH₃COOH
13. Na₂Cr₂O₇
14. K₂Cr₂O₇
The measured adhesional wetting was shown in Fig. 15-41.
Following conclusions was derived from above experiments.
1. Zinc plate which was treated with counter-etching solution containing HNO₃ wets well with water, because it seems HNO₃ in counter-etching solution makes waterabsorbing oxidized film on zinc plate.
2. Zinc plate which was treated with counter-etching solution containing HNO₃ wets well with linseed oil varnish, because it seems alum in counter-etching solution acts on or bonds with water-absorbing oxidized film on zinc plate.
3. Zinc plate treated with K₂SO₄⋅Cr₂(SO₄)₃ wets better with water and linseed oil varnish than that treated with K₂SO₄⋅Al₂(SO₄)₃.
It was proved by experiment that this phenomenon is caused by the difference of Al₂(SO₄)₃ and Cr₂(SO₄)₃ in alum.
4. Zinc plate treated with HNO₃ wets with water better than those treated with other acids used in this experiment. It seems H₂SO₄ is unsuitable for counter-etching solution, because it makes deep pits on zinc plate. Zinc plate treated with HCl wets with water and linseed oil varnish worse than that treated with HNO₃.
Zinc plate treated with CH₃COOH differs much in adhesional wetting with treated time, and CH₃COOH has weaker oxidizing force.
5. Zinc plate treated with oxidizing agents shows the similar wetting to that treated with acid which possesses weak oxidizing force.
6. There are some cases where water evaporates swiftly on the zinc plate. For example, zinc plate treated with HNO₃ or Cr₂(SO₄)₃ shows such phenomenon. We thought that this phenomenon is caused by water-absorbing oxidized film on the zinc plate and is not connected with surface texture of zinc plate.
7. Adhesional wetting of linseed oil varnish is not connected with treated time. And variation in measured value is the smallest of all liquids tested.
8. In adhesional wetting of lithographic ink, zinc plate wets well except those which wets well with water and linseed oil varnish. When zinc plate wets well with lithographic ink, it tends to ooze out.
On the other hand, adhesional wetting of

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