Table I - Selected Tint Etchants

1. 200 g CrO3
20 g sodium sulfate
17 mL HCI
1OOO mL water 		Beraha's tint etch for Al alloys. Pre-etch with10% aq NaOH followed by 50% aq HNO3. Rinse in water, dip immediately into tint etch for 1-5 s. Rinse and dry. Colors matrix grains, outlines second phase particles.
2. 1 g ammonium molybdate
6 g ammonium chloride
200 mL water 		Tint etch of Lienard and Pacque: colors CuAl2 violet. Immerse about 2 min.
3. (a) Stock solution: 1:2, 1:1, or 1:0.5 HCI-water

(b) 100 mL stock solution
plus 0.6-1.0 g potassium metabisulfite

(c) Optional additions:
1-3 g FeCI3, or
lg CUCI2, or
2-10 g NH4FHF

Beraha`s tint etch for Fe, Ni, or Co base heat resistant alloys. Colors the matrix, carbides and nitrides unaffected. Immerse sample in solution at room temperature for 60-150 s. Move sample during etching. Start with lowest HCI concentration; if coloration does not result, increase HCI or etch longer.
4. 50 mL saturated aqueous sodium thiosulfate 3
1 g potassium metabisulfite 		Klemm's I tint etch. Good for many alloys. Immerse 3 min or more for beta brass, alpha-beta brass, and bronzes. Use 10-60 min for alpha brass. Use 40-100 s for coloring ferrite in steels, reveals P segregation and overheating. Longer time produces line etching of ferrite. Etch 30 s for zinc alloys.
5. 50 mL saturated aqueous sodium thiosulfate
5 g potassium metabisulfite 		Klemm s II tint etch. Immerse 6 min or more for alpha brass. lmmerse 30-90 s for steels Reveals P segregation. Good for austenitic Mn alloys. Immerse 60-90 s for tin and its alloys.
6. 5 mL saturated aqueous sodium thiosulfate
45 mL water
20 g potassium metabisulfite 		Klemms III tint etch. Immerse 3-5 min for bronze. Immerse 6-8 min for Monels.
7. 240 g sodium thiosulfate
30 g citric acid
24 g lead acetate
1000 mL water 		Beraha`s lead sulfide tint etch. Dissolve in order given. Allow each to dissolve before adding next (cannot get complete dissolution). Age in dark bottle at least 24 hr before using. Do not remove precipitate. When stock solution turns gray after prolonged storage, discard. Immerse in solution until surface is colored violet or blue. Excellent for copper and its alloys. To color MnS in steels, add 200 mg sodium nitrate (optional) to 100 mL solution; good for 30 min. Colors MnS white. Pre-etch with nital or picral.
8. 21-28% aqueous sodium bisulfite Beaujard and Tordeux`s tint etch for steels. Immerse 10-25 s Reveals grain boundaries and ferrite orientations. darkens as-quenched martensite.
9. 1 g sodium metabisulfite
100 mL water 		Tint etch for lath or plate martensite. lmmerse 2 min (Benscoter et al).
10. 8-15 g sodium metabisulfite
100 mL water 		Darkens as-quenched martensite. Immerse about 20 s.
11. 3-10 g potassium metabisulfite
100 mL water 		Darkens as-quenched martensite. Immerse 1-15 s.
12. 1 g sodium molybdate
100 mL water 		Beraha`s tint etch for cast iron and steels. Add HNO3 to pH 2.5-4.0 (about 0.4 mL). Immerse 20-30 s for cast iron. Fe3P and Fe3C, yellow-orange; ferrite, white. For low carbon steei add 0.1 g NH4FHF, immerse 45-60 s. For medium carbon steel add 0.2 g NH4FHF. For high carbon steel add 0.3-0.4 g NH4FHF. Carbides, yellow-orange to violet; ferrite, white or yellow
13. 3 g potassium metabisulfite
10 g anhydrous sodium thiosulfate
100 mL water 		Beraha's tint etch for iron and steel. Immerse 1-15 min. Colors ferrite, martensite, pearlite, and bainite: sulfides are brightened
14. 0.5-1.0 mL HCI
100 mL water
1 g potassium metabisulfite 		Beraha's tint etch for irons, steels, tool steels. Agitate strongly during etching. then hold motionless until surface is colored; 10-60 s total time. Colors ferrite, martensite, pearlite, bainite. Reveals grain boundaries.
15. 20 mL HCI
100 mL water
0.5-1 g potassium metabisulfite 		Beraha`s tint etch for stainless steels. Immerse 30-120 s with agitation. Colors austenite.
16. Stock solution:
20 mL HCI
100 mL water
2.4 g NH4FHF 		Beraha's tint etch for stainless steels. Before use, add 0.6-0.8 g potassium metabisultite (0.1-0.2 g for martensitic grades). Afer mixing, reagent is good for 2 hr. Use plastic tongs and beaker. Immerse 20-90 s, shake gently during etching. Colors matrix phases.
17. 40-60 mL FeCI3, solution (1300 g/L water)
25 mL HCI
75 mL ethanol 		Hasson's tint etch for Mo. Immerse without agitation for 40-50 s (do not exceed 70 s). FeCI3 can be dissolved in ethanol but etch is slower, 2-3 min. Colors vary with grain orientation.
18. 70 mL water
20 mL H2O2 (30%)
10 mL H2SO4, 		Tint etch for Mo alloys (Oak Ridge National Laboratory). Immerse 2 min, wash and dry. Swab removes colors, produces grain boundary attack.
19. 5 g NH4FHF
100 mL water 		Weck's tint etch for alpha Ti. For pure Ti, immerse a few seconds, longer times for Ti alloys. Colors vary with grain orientation.
20. 39 g NH4FHF
4 mL HCI
100 mL water 		Weck's tint etch for alpha Ti alloys. Immerse for a few seconds. Colors vary with grain orientation.
21. 94 mL 10% aqueous HCI
20 g Cr03 		Tint etch for W (Lehwald et al). Immerse at 55 C (130 F). Use 2 or 3 stages (view between etches) of 15, 10, and 10 min. Pre-etch with grain boundary etch.

Footnotes
1. Additional tint etches are listed in Ref 1 and 2.
2. Whenever water is specified, use distilled water.
3. Maximum solubility of anhydrous sodium thiosulfate (Na2S2O3) is 50 g/100mL water at 20 C (70 F), while that of the crystal form (Na2S2O3. 5H2O) is 79.4 g/100mL water at 0 C (32 F) or 291.1g/100 mL water at 45 C (115 F).

This table accompanied an article, written by George Vander Voort, which originally appeared in the March, 1985 edition of Metal Progress "the monthly magazine of ASM International from 1930 to 1986." It is reproduced here with the kind permission of Margaret Hunt, Editor of Advanced Materials and Processes.
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