US2844530A

US2844530A - Black nickel plating

Info

Publication number: US2844530A
Application number: US640373A
Authority: US
Inventors: Wesley Waclaw Andrew; Knapp Burton Bower
Original assignee: International Nickel Co Inc
Current assignee: Huntington Alloys Corp
Priority date: 1957-02-15
Filing date: 1957-02-15
Publication date: 1958-07-22
Anticipated expiration: 1975-07-22
Also published as: BE564818A; CH368679A; DE1068970B; FR1191571A; GB825031A

Description

July 22, 1958 w. A. WESLEY ET AL 2,844,530

BLACK NICKEL PLATING Filed Feb. 15, 1957 United States Patent() BLACK NICKEL PLATING Waclaw Andrew Wesley, Plaineld, and Burton Bower Knapp, Westfield, N. J., assignors to The International Nickel Company, Inc., New York, N. Y., a corporation of Delaware Application February 15, 1957, Serial No. 640,373 15 Claims. (Cl. 204-40) The present invention relates to a novel bath composition -and process for producing decorative surfaces on metallic articles and, more particularly, to a novel electroplating bath solution and process for the electrodeposition of black nickel finishes on metallic surfaces and to the production of articles of manifacture having black nickel finishes.

It is Well known that metal articles having lustrous black finishes are desirable and suitable for numerous applications and uses, particularly fory decorative purposes and/ or to promote absorption or radiation of heat. Too, matte black finishes are important inproviding nonreecting surfaces in industrial and military instruments of various types, the protoscope being'an example of the former, the naval anemometer an example of the latter. However, black nickel `deposits producedylheretofore have been found unsatisfactory in various applications because of poor abrasion resistance and/or poor adherence of the nickel deposit to the metallic surfaces a'nd/or poor ductility characteristics. Moreover, `prior art black nickel plating processes, in addition to yielding films characterized by unsatisfactory physical properties, have been found difficult to control so as Ato produce a uniform black nickel coating. It has been recognized that factors contributing to difficulties encountered in the controllability of known black nickel plating processes often stem from the comparatively rigid and restrictive operating conditions imposed by such processes, particularly anent pH control, range of concentration of the -constituents of the plating baths, current density limits,

plating times, etc. For example, the normal operating range for the pH of the well-known sulfate-type plating baths, which are perhaps the baths most commonly used in commercial practice, generally falls within the relatively narrow range of about to 6. When the pH of such baths falls below about 5, the nickel deposits often become undesirably dull and unattractive and, as a consequenceA thereof, careful regulation and control of pH values is required. In addition thereto, the concentrations of various constituents commonly employed in sulfate-type solutions must be controlled within rather narrow limits. Too, the permissible current densities employed in many sulfate-type plating baths are often of a narrow and restrictive scope, e. g., about 0.5 to about 1.5 amperes per square foot. It will be appreciated that such. rather 'severe' restrictions with respect to operating conditions It has now been discovered that a decorative, black f finish may be applied uniformly and without difficulty` to metallic surfaces by employing a special electrolytic bath composition and process to produce a vblack nickel electro-deposit which is uniform in color and exhibits an improved combination of properties with respect to abrasion resistance, adhesivity and ductility.

lt is an object of the present invention to provide decorative colored surfaces onmetallic articles.`

Another object of the invention is to provide a durable, substantially permanent black color on metallic surfaces for decorative purposes, to prevent reflectionl ofl light and/or to promote absorption or radiation of heat.

The invention also contemplatesv providing `metallic surfaces with electrodep-osited black finishes characterized by strong adhesivity, good ductility,`and substantial re-` sistance to abrasion. f

lt is also the purpose of the invention to provide nickel and/or nickeleoated materials" with uniform and substantially permanent black nickel finishes which exhibit a superior combination of physical properties as compared to black nickel finishes heretofore known. Y

It is a further object of the invention to provide a novel electrolytic solution for producing tough, permanent, `jet black finishes on metallic surfaces.

The invention further contemplates providing anovel electroplating bath for depositing a decorative jet' black color on nickel and/or nickel-coated materials.

It is another object of the invention to provide a novel electroplating bath for the provision of ductile, adherent and abrasion-resistant black nickel finishes onvmertallc surfaces, particularly nickel and/or nickel-coated materials.

Still another object of the invention is to provide a novel aqueous electroplating bath of special composition for lthe provision of uniform black nickel nisheson metallic surfaces which is conducive to ease of control and facility 'of operation in the electrodeposition of such black nickel finishes. i i It is also an object of the invention to provide a novel process 'for accomplishing the foregoing objects.

lt is likewise Within the contemplation of the instant invention to provide a process for blackening metallic articles which is easily controllable and provides uniform' coatings. o p

Among the further objects of the present invention'is the provision of articles of manufacture with decorative black finishes characterized by an improved combination of properties with respect to abrasion' resistance,I ductility and adhesion. v I

Patented July`l22, 1958 Other objects `and'adt'rantages wll'become apparent l fromthe .following description- .taken in conjunction 'with the accompanying drawing which sets forth a graph depicting the relationship between current density and nickel chloride hexahydrate concentration in the special plating bath contemplated in accordance with the invention.

Generally speaking, the present invention contemplates the electrodeposition of durable black nickel iinishes upon metallic articles, particularly nickel and nickel-coated articles, by subjecting the metallic articles to the action of an aqueous, acidic electroplating bath containing nickel chloride hexahydrate, ammonium chloride, sodium thiocyanate and zinc chloride, the nickel chloride hexahydrate concentration and current density being related such that the correlation falls within the shaded area ABCDA of theaccompanying graph. The. black nickel iinishes producediinaccordance with the concepts of the instant inventionfare characterized by a highly satisfactory combinationof 1physical properties, including abrasion resistance, ductility, and-adhesivity of the black nickel deposit to the'metallic'snrface treated. Moreover, as shown by the graph, nickel chloride-hexahydrate-current density relationships falling outside the shaded rarea of the graph result ininferior black nickel deposits. For example, a nickel chloride heXahydrate-current density relationship above the shaded area results in irregular, grey deposits; relationship falling below the shaded area results in darkgrey deposits. t

i The constituentsV of our electroplating'solution can be varied over relatively Wide range of Aconcentration and this factor isV an extremely important commercial consideration because itadvantageouslyassists in minimizing the prior diiiicultiesencountered in controlling black nickel plating-processes; The concentrations of the respectivefcomponents ofv our aqueous plating bath are maintained as follows: nickel chloride (NiCI2.6H2O), at least about 50 g. p.` 1. (grams per liter), e. g., 50 to about 165 g. p. l.; ammonium chloride (NHiCl), about 7.5 to about 45 g. p. l.; sodium thiocyanate (NaCNS), about 7.5 g..p. l. to-about 30 g. p. l.; andzinc chloride (ZnClZ), aboutlS to about 6tlg. p. l. Preferably, the bath contains about 60 to about 90 g. p. l. of nickel chloride hexahydrate, about l to about 30g. p. l. of ammonium chloride, aboutto about 20 g. p. l. of sodium thiocyanate, and about` to about 50 g. p. l. of zinc'chloride. We have'found that it is important within the principles of the instant invention that the concentrations of ammonium chloride and zinc chloridenot fallbelow-a minimum ofabout 7.5. g. p. l. andapproximately l5 g. p. l., respectively. Amounts of ammonium chloride below about 7.5 g. p. l. produce unattractive, rough grey deposits. Likewise, when rthe minimum'A amount of zinc chloride falls below about l5 g. p. l., an, undesirable light grey color results.

One of the attendant advantages and features of the present,v invention is that uniform black inishesv are obtained with a minimum amount of regulation and control during the electrodeposition operation. Not only does our plating bath permit of an appreciable latitude in varyingrtheA concentrations of the respective constituents. but the pH, current density and platingtime may also be varied over comparatively wide ranges. With `respect to pl-I, the data set forth in Table I hereinbelow illustrates that the pH can be varied over the relatively 4wide range of from at least as low as pH 2.3 to at least about pH 5.5. The electroplatingsolution of the present invention containing nickel chloride hexahydrate, ammonium chloride, sodium` thiocyanate and zinc chloride generally has i afpI-Ipvalue of the order of 5 toabout 5.5 If it is desired to operate at lower pH values, the pH can be readily adjusted by addingto vthe bath a small amount of acid, preferably hydrochloric acid in an` amount vup to about 0.5: milliliter per liter ofelectroplating solution. An equivalent amount of sulfuric acid can be used but is less preferred.

4 Table I Black nickely plating 'solution NlClnHeO e p.l NH4C1 e p. 1 30 NaCNS z p. l-.. 15 ZnClz g. p. 1 30 Plating conditions Temperature room. Cathode Wrought nickel. Anode wrought nickel.

Current Time, Run No. pH Densigy, Minutes Cathode Appearance 5. 5 l. 5 30 Good Black Color. 5.0 1.5 30 Do. 13.6 1.5 3() Do. 12.3 1.5 30 Do.

l pH obtained by adding hydrochloric acid.

edly advantageous and particularly beneficial in providing an easily controllable process.

Another advantage of the present invention is that substantially thick black nickel deposits can be obtained if desired under a given set of operating conditions since the electrodeposition. process can be conducted for relatively long periods of time without deleteriously affecting the attractive black appearance of the electrodeposited lm. Generally, thereis normally a minimum time interval required to produce a black `film at a particular current density. Plating periods below this minimum value usually result in dark films having some color interference. Whengthe platingperiod is allowed to continue for relatively long periods of time beyond the minimum time interval, a thicker iilm develops but it remains black in color. `This factor permits` the build-up of thick black deposits onthe-metallic surface being treated and byso doing it serves a twoffold purpose. First, careful regulation of therplating period above a minimum time interval substantially obviatedand secondly, the thick depositssosobtained materially assist in providing good abrasion resistance. Table II hereinbelow sets forth byway vofillustration various plating periods that may besuitablyemployed for current densities of 1.5 a. s. f. and higher.

Table l1 Black nickel plat-ing'solution:

l NiClaHeQ as indicated.

` NH4CT. g. p. NaCNS 15 g. p. l. '.ZnClay 30 g. p l Plating conditions Temperature room.- Cathode wrought nickel. Anode wrought nickel.

Current Time, NiCla.6HaO, Cathode Appear- RunJNo.: pH. Density, Ming. p. l. anco l A l a. s. f. utes 5 5.3 1.5 7.5 75' GoodDarlr .Color But Some Interference Color. 5. 3 1.5 15 75 Good Dark Black. 5.3 1.5 30' 75 D0. 5.5 1.5 15 75 Do. 5.5V 1.5 30 75 Do. y 5:2 1.5 30 6U Do. 5:2` 3.0 15 105 Do. 5. 2- 3. 0 30 t 105 Do. 5.1 3.0 30 105 Do.A 5; l 6. 0 7'. 5 150 Du. 5.1 6.0 30 150 Do.

1' Nickel-plated steel cathode.

In '.runla.I darkcolor was obtainedhaving some interferencecolor. The platingtime was7.5 minutes indicatingithat a Vborderlinetirne had elapsed forv the deposition of .a good darkl black color. When the plating time was increased to `l5' minutes as shown by run 6, a gooddark blackliinishwasrobtained. In run 7, the development of good black film of increasing thickness was still continuing after a plating period of 30 minutes. If short plating periods will serve the intended purpose or are required by economical and commercial considerations, plating intervals at least as low as 7.5 minutes can be satisfactorily employed in accordance with the present invention since the current density can be increased to at least about 6 a. s. f. This feature is illustrated by run 14 of Table II. Again, a thicker deposit could be obtained by extending the plating period of run 14, for example, to 30 minutes as shown in run 15 of Table II.

We have also discovered that the abrasion resistance and adhesion of black nickel finishes can be further improved by subjecting the surface of the material to be blackened to a pre-treatment operation wherein an initial or preliminary metal electrodeposit, preferably nickel, is applied to the surface prior to the aforedescribed black plating treatment. It has been found that when the pretreatment operation is employed, black finishes are obtained having a markedly improved combination of superior abrasion resistance and adhesion as compared to black finishes heretofore known. It is preferred to provide the initial nickel electrodeposit from an acid-nickel chloride-bath containing not more than about 350 g. p. l. of nickel chloride hexahydrate, the pH of the bath being not more than pH 3. Preferably, the pre-treating bath contains up to about 35 g. p. l. of boric acid, up to about 40 g. p. l. of hydrochloric acid and about 150 to about 340 g. p. l. of nickel chloride hexahydrate.

A preferred acid-nickel chloride pre-treatment operation comprises immersing the article to be treated in an aqueous bath solution containing about 150 to about 240 g. p. l. of nickel chloride hexahydrate and about 30 toy about 40 g. p. l. of hydrochloric acid. The bath is maintained at a temperature of about 60 F. to about 80 F. at a pH of about to about 0.5. The article to be plated is treated anodically for about l to about 3 minutes and then cathodically for about 5 to about 10 minutes while employing suitable current densities of about 20 to about 40 a. s. f.

Of course, other pre-treatment operations can be satisfactorily employed to provide the preliminary nickel electrodeposit. For example, a nickel electrodeposit from a pre-treating bath containing about 30 g. p. l. of boric acid and about 300 g. p. l. of NiCl2.6H2O has given excellent results. The operating conditions for this bath were as follows: temperature, 140 F.; pH, about 2; and current density, about 50 a. s. f. A small amount of antipitting agent, about 0.2 g. p. l., sold as Duponol ME, was

ladded to the bath.

The data tabulated in Table III is illustrative of the combination of excellent adhesion and abrasion properties obtained when using the acid-nickel chloride pretreatment process and affords a comparison of. results when wrought nickel and nickel-plated steel panels were subjected to known conventional pre-treating processes as well as to thev acid-nickel chloride pre-treatment process. The acid-nickel chloride treatment involved treating the materials in an aqueous bath maintained at about 75 F. and containing about 180 g. p. l. of nickel chloride (NiClgHzZ) and approximately 36 g. p. l. of hydrochloric acid. An electric current was passed therethrough at a current density of about 30 a. s. f. and the articles were treated anodically for approximately 2 minutes and then cathodically for about 6 minutes. The panels were rinsed in clean water and then subjected to the action of our plating bath under conditions set forth in Table IH herein. Each panel was then tested for both abrasion resistance and adhesivity. The abrasion test consisted of revolving a pencil eraser in contact with the surface of the respective panels at about 625 revolutions per minute with sufiicient pressure to deform the eraser. The test was conducted for periods of 1, 3, 5, 10 and 20 seconds on different portions of the panels. With respect to the adhesion test, all runs were conducted by subjecting each panel to a severe bend test wherein a .freev bend was applied through an angle of which gave a bend with a radius of about S/ inch to 1A inch."v v

Table III Black nickel plating solution NiClzHzO g p. 1- 75 H401 Q p. 1- 80 NaCNQ g n.1-- 15 Znfln Z p.1 30 Plating conditions:

Temperature room.

ode wrought nickel. nI-T 5.5 urrent density 1.5 a. s. f. Timo 30 minutes.

Abrason Test,l Run Pre- Seconds l Adhesion N o. Cathode Material treat- Bend ment 1 Test 16 Wrought Nickel.. P E G F Poor. 17 do POS E G F Fairly Good 18 do PCH E G F Very j Poor 19 do PCA E Exceli lent. 20 Nickel-Plated None EV G F F Very Steel. Poor. 21 do CS E G Fairly Goud. 22 .do CH E G F Fair. 23 do CA E Excellent.

lP-pumice scrub; C-cathodic alkaline clean; S-25% H2SO4 dip; EIC-15% (vol.) HC1 dlp; A-Acid-nickel chloride treatment.

2 E, G, F and P represent ,the rating of excellent, good, fair and poor,

respectively.

It will be noted that in only runs Nos. 19'and 23 was a rating of excellent (E) obtained for bothv abrasion-resistance (20 second periods) and adhesivity and in each of these experiments the material being plated was subjected to the acid-nickel chloride pre-treatment process described hereinbefore. Although a severe bending test was applied for determining the adhesive qualities of the respective finishes, there was no indication of chipping, peeling, flaking, etc., of the black coating formed in accordance with our invention and using our aforedescribed pre-treatment process. The data concerning the 1bend test of 180 also serves to illustrate that the black finishes produced in accordance with our invention, while utilizing the preferred pre-treatment process (runs Nos. 19 and 23), are highly ductile.

Metals other than .nickel which can be satisfactorily used as the preliminary metal electrodeposit include copper, silver, cobalt, chromium, lead, cadmium, zinc, tin, antimony, bismuth'and gold. Alloys such as cobaltnickel, tin-bismuth, antimony-bismuth and brass can also be suitably employed as preliminaryv metal electrodeposits.

For many purposes, black matte nishes are also desired. In such instances the material to be plated is given a matte surface by mechanical, chemical or other means. However, black matte finishes provided'on such surfaces heretofore have exhibited the undesirable effect of lacking adhesivity. In accordance with the present invention, black matte finishes are easily achieved and the finish is strongly adherent. i

The present invention can be employed to provide black finishes on a Wide variety ofV foundation metals and/or alloys such as stain-less steel, steel, vcopper alloys, cast iron, precious metals, and alloys thereof, etc., and is particularly applicable for producing black decorative coatings on nickel and/or nickel-coated materials, e. g., wrought nickel, electrodeposited nickel. The instant invention is suitable for such applications as nickel-plated steel, baking pans, office machines, name plates, jewelry, photographic equipment, etc. V

It will be apparent from the foregoing that the instant invention provides a novel aqueous electrolytic bath and an electrcdeposition process which is easily controllable in providing jet black finishes on metallic surfaces,

Since vconcentrations `ot' nickel chloride,

Nfinishes .as well. aslustrous Yblack finishes.

ammonium chloride, sodiumthiocyanate, and zinc chlorideA mayb'e suitably varied over relatively wide ranges and since a wide latitude is permittedin' variations of pl-I'values, cur- Vvrent densities and plating times, careful control and fregulation'ofthe,process is substantially minimized. {avillabe' readilyapparent that the flexibility in operating "conditions ofthe 'instant invention providesl the art-With a process 'which mayvbewconveniently adapted to fulll `aparticular 'need/for' requirement. For examplefif an attractiVeblack-nish isvdesiredin a-minimum time interval, a'suitably high' currentdensity, e. g., 6 or 7 a. s. f., may be: satisfactorily employed. If a thick black deposit l.is desired, `the plating operation can be conducted for 4but the Vcontent of nickel chloride in the solution can be 'provided by'any suitable means.

`Although the present invention has been described in conjunction with preferred embodiments, it'is to be understood that modifications and variationsmay be resorted yto without departing from the spirit and scope .lof thel invention, as-those skilled in the art will readily understand. Such moditicationsand variations are conlsidered to be withinA the purview and scope of the inven- Ation .and appended claims.

to about 30 g. p. l. of ammonium chloride, about 10 g. p. l. to about g. p.l l. of r.sodium thiocyanate and about v-20 g. p. l. to about 50 g. p. l. of zinc chloride.

'2. A bath for electrodepositing black finishes 'on metallic surfaces and comprising an aqueous, acidic solution containing about 50- g. p. l. to about 165 g. p. l. of nickel chloridehexahydrate, from 7.5 g. p. l. to about 45 g. p. l. of ammonium chloride, about 7.5 g. p. l. to abouti 30,1 g. p. l. of sodium thiocyanate and from l5 g. p..l. to about 60 g. p. l. of zinc chloride.

`3. A bath vfor electrodepositing black finishes on metalliclarticles and comprising an aqueous, acidic solutionacontaining at least about 50 g. p. l. of nickel chloride hexahydratafrom 7.5 g. p. l. to about 45 g. p. l. of am- Emonium chloride, about 7.5 g. p. l. to about 30 g. p. l. of sodium thiocyanate andlfrom l5 g. p. l. to about 60 g. 'pf l.- of zinc chloride.

`4. A'process for electrodepositing attractive black linishes on metallic articles which comprises subjecting the article to be blackened to the action .of an aqueous electroplating solution having a-pH Within a range of at least as low as about 2.3 and up to about 5.5 and containing from 7.5 g. p. l. to -about 45 g. p. l.- of ammonium chloride,-fabou`t 7.5 g. p. l.to about 30 g. p. l. yof sodium thiocyanate, from l5 g. p. l. to about' 60 g. p. l. of zinc chloride, vandi nickel chloride hexahydr'ate, the nickel chloride LheXahydrate concentration and current density being re- `lated' asuch. that theV correlation'falls within the shaded arealA'BCDA Aof the accompanying graph.

5. A method as described in claim 4 wherein the metal 'to be blackened has anickel surface.

6. An easily ycontrollable process for electrodepositing=substantially permanent and uniform black, vdecorative finishes `on metallic articles whichcomprises lsubjecting the article to be blackened `to the 'action ofan l'aqueous electroplating solution having a pH within 'a ran'geoflat least as low as about 2.3 up to about 5.5 v*and .containing about l5 g..p.`l. to'about 30 g. p. l. of ammonium chloride, about l() g. p. l. to about 20 g. p. l. of

sodium thiocyanate, about 20 g. p. l. to about 50 g. p. l.

'of zinc chloride, and nickel chloride hexahydrate, the

tractive black finishes on metallic articles which comprises 'the steps of pre-treating the article to be blackened by providing an initial metal electrodeposit thereon and then' subjecting the pre-treated article to the action of an aqueous electroplating solution having a pH Within a range of at least as low as about 2.3 up to about 5.5

-and containing from 7.5 g. p. l. to about 45 g. p. l. of

ammonium chlorideabout 7.5 g. p. l. to about 30 g. p. l.

Vofsodium thiocyanate, from 15 g. p. l. to about 60 g.V p. l.

of zinc chloride, and nickel chloride hexahydrate, the concentration of said nickel chloride hexahydrate being related to the current density employed such that the correlation thereof falls within the shaded area ABCDA of the accompanying graph.

9. .A method as described in claim 8 wherein the initial metal electrodeposit is nickel.

10. A method as described in claim 9 wherein the metal to be blackened is nickel-surfaced.

11. An easily controllable process for providing dur able, uniform and attractive black finishes on metallic articles which comprises the steps of pre-treating the article to be blackened by providing an initial metal electrodeposit lthereon and then subjecting the pre-treated article -to the action of an aqueous electroplating solution having a pH within a range of at least as low as about 2.3 and up to about 5.5 and containing from l5 g. p. l. to 30 g. p. l. of ammonium chloride, about l0 g. p. l. to

about 20 g. p. l. of sodium thiocyanate, from 20 g. p. l.

metallic articles which comprises the steps of immersing the metallic article in an acid-nickel chloride electrolyte containing acid and not more than about 350 g. p. l. of nickel chloride hexahydrate, the pH of the electrolyte being not more than about pH 3 to thereby provide the 'said metallic article with an initial electrodeposit of nickel, and then subjecting the metallic article so treated to the action of an aqueous electroplating solution having a pH within a range of at least as 10W as about 2.3 and up to 5.5 and containing from 7.5 g. p. l. to about 45 g. p. l. of ammonium chloride, about 7.5 g. p. l. to about 30 g. p. l. of sodium thiocyanate and from l5 g. p. l. to about 60 g. p. l. zinc chloride, and nickel chloride hexahydrate, the concentration of said nickel chloride hexahydrate being related to the current density employed such that -the correlation thereof falls within the shaded area ABCDA of the accompanying graph.

14..AY process 4as describedinclaim'l-S wherein the said acid-nickel chloride electrolyte contains up to 35 g. p. l. of boric acid, up to about 40 g. p. 1. of hydrochloric acid and about 150 g. p. l. to about 340 g. p. l. of nickel chloride hexahydrate.

15. A process as described in claim 14 wherein the said acid-nickel chloride electrolyte contains about 150 to about 240 g. p. l. of nickel chloride hexahydrate and about 30 to 40 g. p. 1. of hydrochloric acid and the article is treated in said electrolyte anodically for about 1 I10' r to 3 minutes and then cathodically for about 5 to 10 minutes and the current is passed through the said electrolyte at a current density of about 20 a. s. f. to about 40 a. s. f.

References Cited in the file of this patent UNITED STATES PATENTS 2,679,475 Singler May 25, 1954 wmlili mmomm animali@ oi @ommen Patent No 29 844g 53C July 22, l958 Waelaw Andrew Wesley et alc lt is hereby certified that error appears in theprinbed specificaj/ioJn of isne above lnum`r ered pateniJ requiring correction and 'bha-t. the said Letters Patent should read as corrected below.

"(NiC12ei-2o)," read fm (Nioigngo), um; @011mm "Black nickel plating solutionz" oolwnn 5', line 60, for

Column 3,n line 36j foi` ./JI., line 50, Table ll, under June heading second oinmle,y for NifllCM read NHACl ew; NiClga'flgZ'Y read n QNiClQHQO) mo Signed and sealed this 16th day of December l958 (SEAL) Attest: ROBERT o. WATsoN KNEL H0 AXLNE Commissioner of Patents;

Attestinlg cer

Claims

4. A PROCESS FOR ELECTRODEPOSITING ATTRACTIVE BLACK FIN ISHES ON METALLIC ARTICLES WHICH COMPRISES SUBJECTING THE ARTICLE TO BE BLACKENED TO THE ACTION OF AN AQUEOUS ELECTROPLATING SOLUTION HAVING A PH WITHIN A RANGE OF AT LEAST AS LOW AS ABOUT 2.3 AND UP TO ABOUT 5.5 AND CONTAINING FROM 7.5 G. P. L. TO ABOUT 45 G. P. L. OF AMMONIUM CHLORIDE, ABOUT 7.5 G. P. L. TO ABOUT 30 G. P. L. OF SODIUM THIOCYANATE, FROM 15 G. P. L. TO ABOUT 60 G. P. L. OF ZINC CHLORIDE, AND NICKEL CHLORIDE HEXAHYDRATE, THE NICKEL CHLORIDE HEXAHYDRATE CONCENTRATION AND CURRENT DENSITY BEING RE-