original pot metal 1940 Buick grille needing restoration and chrome plating

Follow a Part from the Start: Pot Metal Grille

July 7, 2015 by Josh - No Comments

If one is to study the history of automotive design, they will find that from the earliest car to the newest cars, everything has evolved from mechanical design to fluid design.  Early on form followed function, but once the popularity and affordability of the car took off, the roles became reversed.  During the early 20th century, automotive manufacturers and more specifically coach builders, were looking for ways to streamline the cars they were producing.  As the designs became less mechanical and more flowing, the parts adorning the cars became even more complicated to produce.

At that time, a common practice was for a tool and die maker to shape the parts from wood and develop a way to stamp or cast the part.  Some early castings were entirely made up of iron, brass, or lead.  As costs began to rise and the parts were being produced in mass quantities, the industry was in need of a more economical way to cast these unique pieces.  This inevitably led to the development of what is known as pot metal.

So what exactly is pot metal?  In a nut shell, manufacturers would gather up any scrap metal with a low melting point that was left over from production and melt them all together in a large pot.  This liquid metal consisting of everything from copper, lead, iron, tin, magnesium, aluminum, and most notably zinc (pot metal is also referred to as zinc die cast), would then be used in the casting process to create the needed parts.  It was inexpensive and made the most sense at the time.  The only problem is, the longevity of pot metal is short.

Why is the longevity of pot metal so short?  Instability.  There is an old saying that some things get better with age, this however is not the case for pot metal.  The older it gets the more likely it is to completely fall apart and be deemed totally unusable.  Most of this instability is derived from the casting process when air becomes trapped creating bubbles within the casting due to the differing melting points of the various metals.  Plus, all of these metals are vulnerable to acids and contaminants found in the air.  As a result, pot metal is easily broken, bent, cracked, and most commonly pitted.

Sadly, some of the most beautiful cars produced from the 1930’s through the 1960’s are covered in some of the worst pot metal ever cast.  The worst part is, pot metal is not easily repaired or re-plated.  If it is broken, misshapen, or pitted, it is incredibly time consuming and tedious to repair.  Not to mention, one could successfully repair the pot metal and then fight getting it to seal up and chrome plate without any blistering.

Luckily, here at Advanced Plating we are fully equipped to handle pot metal and all of the troubles that come with it.  As a matter of fact, at least 75% of the automotive parts we perform restoration services on are pot metal.  Cracks, broken pieces, and most pitting are all problems that we are well versed in and able to handle.  In this edition of Follow a Part from the Start, we will show you the rigorous efforts that go into the restoration and plating of a pot metal grille from a 1941 Buick.  This way you can see firsthand what it takes to bring pot metal back from unusable to show stopping.

original 1940 Buick grille needing restoration and chrome plating

This is an original 1941 Buick grille as it was when it arrived at Advanced Plating for repair, restoration, and chrome plating.

original 1940 Buick grille needing restoration and chrome plating

Here is a close up to show the level of the deterioration and pitting of the vintage grille.

original 1940 Buick grille needing restoration and chrome plating

As mentioned, a downfall of pot metal is that it becomes brittle and can crack. Here one of the main supports has cracked and broken away completely from the horizontal base bar.

original pot metal 1940 Buick grille needing restoration and chrome plating

Interestingly enough, electro-stripping will remove the chrome plating, but it will not remove paint. Originally this grille was accented with paint in some of the fine lines and pockets of horizontal base strip. This old paint is removed by lightly media blasting those areas.

original pot metal 1940 Buick grille needing restoration and chrome plating

Once the paint is removed, the grille is wired up and placed in the sulfuric acid tank for electro-stripping.

original pot metal 1940 Buick grille needing restoration and chrome plating

After the proper amount of time has passed, the grille is removed from the sulfuric acid tank and a raw pot metal part is the result.

original pot metal 1940 Buick grille needing restoration and chrome plating

Now that the grille has been stripped to raw pot metal, it goes back to the blast cabinet for further media blasting. Blasting after electro-stripping helps create a nice consistent finish to work with and ensures the part is stripped of any old plating, paint, or contaminants.

original pot metal 1940 Buick grille needing restoration and chrome plating

With all stripping complete, the grille is ready to hand off to the polishing department for repair and restoration.

original pot metal 1940 Buick grille needing restoration and chrome plating

In a raw state all of the pitting and deterioration of the pot metal is even more visible and prevalent than before. It is not uncommon for pot metal parts to look worse after stripping than they did prior.

original pot metal 1940 Buick grille needing restoration and chrome plating

In order to create stability within the part before extensively working it over, the broken brace must be repaired first.

original pot metal 1940 Buick grille needing restoration and chrome plating

Before the repair can be made to the broken support bar, a cyanide copper base is required to promote adhesion of the repair and ensure the pot metal is sealed up and will not blister.

original pot metal 1940 Buick grille needing restoration and chrome plating

At this time, the repair will not be ground smooth and is purely there to hold the grill together. After the initial grind and and trip through cyanide copper, the break will be fully repaired and this will be removed.

original pot metal 1940 Buick grille needing restoration and chrome plating

Now that this half of the grille has some strength, the initial grind is performed. The horizontal bars have multiple faces and contours, so the polisher starts by using a large grinder on the wide top face of the bars.

original pot metal 1940 Buick grille needing restoration and chrome plating

The same grinder is used to cut flat the leading edge face of the horizontal bars as well. When cutting down the pot metal, it is ground as far as possible without loosing any detail or making the part too thin.

original pot metal 1940 Buick grille needing restoration and chrome plating

On the band surrounding the horizontal bars, the face is ground with the same grinder and then a small angle grinder is used to bevel out a crack will need filled.

original pot metal 1940 Buick grille needing restoration and chrome plating

Here is the grille half once it has been completely ground, with the except of the curved contours.

original pot metal 1940 Buick grille needing restoration and chrome plating

A cartridge roll that is almost the same width as the curved contour is then used to sand down these stylized faces.

original pot metal 1940 Buick grille needing restoration and chrome plating

Now that the initial grinding phase is complete, both grille halves are sent to the racking department where they are strategically wired up and hung for cyanide copper plating.

original pot metal 1940 Buick grille needing restoration and chrome plating

As mentioned previously, now that the cyanide copper base is once again on the grille, the crack can be repaired with lead solder.

original pot metal 1940 Buick grille needing restoration and chrome plating

Also at this time, further repair is made to the broken support bar by soldering on the visible face of the support.

original pot metal 1940 Buick grille needing restoration and chrome plating

The small angle grinder is then used to smooth out the repair over the crack on the surround.

Once sanded smooth, it is hard to tell that it was ever cracked. It is okay that the cyanide was sanded off in the process. The main thing is that the layer between the solder and the pot metal is cyanide copper.

original pot metal 1940 Buick grille needing restoration and chrome plating

The repairs to the broken support are also sanded at this time, only using a cartridge roll instead of the angle grinder. The cartridge roll will allow more freedom for shaping the area.

original pot metal 1940 Buick grille needing restoration and chrome plating

Not only did the polisher smooth out the repair on the outer face, he has also smoothed out the visible faces as well.

original pot metal 1940 Buick grille needing restoration and chrome plating

Since repairs were made to the main support, the polisher checks the fit of the center divider to the grille halve to ensure that everything is true and fits properly. He will also scuff up the rest of the grille at this time and send it to the plating line for acid copper.

original pot metal 1940 Buick grille needing restoration and chrome plating

All grille parts are now in the acid copper stage. Acid copper is a heavier deposit than cyanide copper and it is softer. Acid copper will now be used to help remove waves, imperfections, and inconsistencies.

original pot metal 1940 Buick grille needing restoration and chrome plating

Taking a slightly less aggressive approach to sanding, the polisher now uses a DA with finer grit paper to sand down the whole grille and reveal any imperfections.

original pot metal 1940 Buick grille needing restoration and chrome plating

The same attention to detail is exercised with the DA that was demonstrated with the grinder, sanding on each face separately and with precision to retain crisp edges and definition of contours.

original pot metal 1940 Buick grille needing restoration and chrome plating

The grille is now ready for another round of acid copper plating.

original pot metal 1940 Buick grille needing restoration and chrome plating

From this close up you can see how the bars are taking shape and the pitting is being eliminated. At this point, it will not be much longer before the part is ready to chrome.

original pot metal 1940 Buick grille needing restoration and chrome plating

Back from acid copper, the grille will go through the same sanding steps once again. The only difference…this time the grille will be buffed out bright and ready for chrome plating.

original pot metal 1940 Buick grille needing restoration and chrome plating

Sanded out to a 320 finish, the polisher carefully buffs out all of the visible surfaces to a mirror finish in preparation for chrome.

original pot metal 1940 Buick grille needing restoration and chrome plating

Here you can see the grille is polished out bright and ready for the chrome plating process.

original pot metal 1940 Buick grille needing restoration and chrome plating

Before final plating can begin, the part is racked up and cleaned in an alkaline cleaner using brushes and scrub pads to ensure that all compounds, grease, and oils are removed from the part. If anything is missed, it will show up as a flaw after plating.

original pot metal 1940 Buick grille needing restoration and chrome plating

After cleaning, rinsing, an acid etch, and another rinse, the parts are placed in the nickel tank for the appropriate amount of time.

original pot metal 1940 Buick grille needing restoration and chrome plating

Now that just the right amount time has passed, the grille is removed from the nickel tank and rinsed multiple times.

original pot metal 1940 Buick grille needing restoration and chrome plating

Last stop is the chrome tank. The grille is placed in the chrome tank for a couple of minutes and when removed from the tank, the grille has a yellow-gold look from the solution. Don’t worry though, it rinses right off to reveal a beautiful finish.

original pot metal 1940 Buick grille needing restoration and chrome plating

See! Just like we told you, the solution rinses off and a brilliant chrome finish is revealed. This part is now ready for inspection.

original pot metal 1940 Buick grille needing restoration and chrome plating

The end result is a true piece of jewelry that will adorn the front of a vintage 1940 Buick for a look that will be hard to miss.