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Plat­ing The­ory

Elec­tro­plat­ing can be de­fined as the de­posit of a very thin layer of me­tal onto a base me­tal in or­der to en­hance or change its ap­pear­ance. Un­like paint­ing, where the new de­posit is sprayed on, the chrome (and as­so­ci­ated ma­te­ri­als) are ap­plied through the use of an elec­tri­cal cur­rent, hence the term ‘elec­tro­plat­ing.’

A plat­ing bath is the name for what is es­sen­tially a gi­ant tank, many of which are used through­out the chroming process. The baths are filled with a liq­uid that con­tains the de­sired me­tal dis­solved within it — which could be sil­ver, gold, nickel or another me­tal.

The plat­ing–bath so­lu­tion serves as a con­duc­tive medium, utiliz­ing a low DC volt­age. The me­tal item that is to be plated is sub­merged in the plat­ing bath, and a low-volt­age DC cur­rent is ap­plied to the bath.

The elec­trolytic process then causes the dis­solved me­tal ions to at­tach to the sur­face of the me­tal to be plated. The thick­ness of the elec­tro­plated layer is de­ter­mined by the time the item spends in the plat­ing bath while the cur­rent is be­ing ap­plied, and the amount of cur­rent used.

Some­times the shape and con­tour of the item can af­fect the thick­ness of the plated layer. Me­tal ob­jects with sharp corners and edges will tend to have thicker plat­ing on the out­side corners and thin­ner plat­ing in the re­cessed ar­eas. This is due to the corners be­ing more ex­posed, there­fore at­tract­ing more par­ti­cles.

The Price of Plat­ing

The price of elec­tro­plat­ing ser­vices is de­ter­mined by nu­mer­ous fac­tors such as the type of me­tal used for plat­ing (i.e. gold, sil­ver, chrome, etc), the de­sired thick­ness of the plat­ing, the base me­tal (i.e. steel, cop­per al­loys, alu­minum), the rough di­men­sions of the ob­ject to be plated, and the num­ber of items to be plated. As an ex­am­ple, nickel costs around $16,000 per tonne — as a rough guide­line, on the av­er­age ’50s US clas­sic car, around 12kg of nickel is used.

What many for­get, how­ever, is that since the plat­ing process does not hide or mask sur­face im­per­fec­tions, plenty of prepa­ra­tion time is re­quired to en­sure a flaw­less fin­ish be­fore the plat­ing process it­self has even be­gun.

Most ve­hi­cles of the chrome era have more than their fair share of dents and scrapes in the trim­work, and re­mov­ing them is not a straight­for­ward task. In­deed, it’s one that in­volves plenty of skill, and an even greater amount of time — which all adds to the cost in­volved, in the same way that panel beat­ing and prepa­ra­tion add to a paint job.

Ask any­one who’s had a bumper from a ’50s US cruiser chromed how much work was in­volved in get­ting the bumper straight and tidy prior to plat­ing, and you’ll soon see where a large pro­por­tion of the fi­nal cost goes — yet it’s amaz­ing how many seem to for­get all about the prepa­ra­tion time when it comes to set­tling the even­tual bill.

It also pays to re­mem­ber that as each tank used in the elec­tro­plat­ing process has a cur­rent sent through it to ac­ti­vate the so­lu­tion within, the monthly power bill for the plat­ing busi­ness can be as high as $30,000 — another cost that most of us would never even have dreamed about.

Next the old chrome is re­moved in a cold caus­tic bath, this time elec­tri­fied to 12 volts with a re­verse charge. That sees the old chrome come off the item with sur­pris­ing ease in just 10 min­utes. The old chrome and stripped met­als are not re­cy­clable. Get­ting rid of them is a ma­jor ex­pense for any elec­tro­plat­ing com­pany, and it’s con­trolled by lo­cal coun­cil by-law re­quire­ments (un­der trade waste con­sents leg­is­la­tion).


9That next bath is a two-minute dip in a cold cyanide so­lu­tion, in which the parts are elec­tro-cleaned by hav­ing a re­verse charge passed through them. Again, a fresh wa­ter rinse is per­formed prior to the next stage. The items must not dry out be­fore be­ing trans­ferred to that next stage; if they do, blotch­ing will oc­cur, of­ten the sign of a lack of care dur­ing the process. Thank­fully, Ge­orge and his team check the items at ev­ery stage, en­sur­ing only the best-pos­si­ble fin­ish is supplied to the cus­tomer.

A cold bath of 10 per cent sul­phuric acid is then used for two min­utes to give the sur­face a key for the next step to etch to. This is es­sen­tial to en­sure that the cyanide-based al­kali cop­per used next will ad­here to the item as much as pos­si­ble. At­tached to the sides of the bath are bas­kets with blocks of pure cop­per (an­odes). When dis­solved in the so­lu­tion, the par­ti­cles are at­tracted to the pos­i­tively charged item, and soon a thin coat of cop­per cov­ers the whole thing. The cop­per is less than one mi­cron thick, and acts as a primer-sealer to key-in the next layer of plat­ing.

Again the item is rinsed, then dropped into a 10-per-cent acid etch for 10 sec­onds, fol­lowed by a fur­ther rinse.

So far, the com­pounds used in the process are rel­a­tively low cost. But the nickel sul­phate the items spend the next 60 min­utes sit­ting in is no­tably more ex­pen­sive, in fact, it’s the dear­est con­sum­able of the whole pro­ce­dure. Af­ter 60 min­utes with a six-volt cur­rent, a 45-mi­cron coat­ing will be ap­plied to the item. This is the most im­por­tant part of the whole process, as it’s the nickel that gives the fin­ished prod­uct its shine. Of­ten the dif­fer­ence be­tween cheap chrome and good chrome is the amount of time the items sit in this bath for. The dif­fer­ence is no­tice­able to the naked eye by the depth of colour in the fin­ished item.

A rinse then re­moves any ex­cess residue and pre­pares the item for the chrome it­self, which is a com­par­a­tively cheap and quick part of the whole pro­ce­dure. De­spite be­ing or­ange, the chromic acid is what gives the bluish look, and af­ter just four min­utes in the bath with a 12-volt cur­rent, a three-mi­cron coat­ing will be fixed to the item. Again, the balls in the tank are there solely for in­su­la­tion pur­poses. The tank it­self is tested twice daily for cor­rect chem­i­cal lev­els, bright­ness and con­di­tion, and is stirred through­out the day. Af­ter all, the chrome is a heavy me­tal, so it tends to sink to the bot­tom when left for long pe­ri­ods.

A full re­fill of all the tanks would set Ge­orge back around $365,000, but thank­fully they don’t re­quire com­plete re­place­ment all that of­ten.


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