The Color of Screws

patlaw

Mike
Corporate Member
I do some equipment restoration as a hobby. Looks are important. Take a look at these two screws. One is shiny silver, the other is darker. The ones in the equipment are the darker ones. Most of the screws I buy are the shiny ones. Since I didn't buy either of the screws in this picture, I don't know anything about them. What finish is on the darker ones? I'm sure they're the cheapest ones available. The pictures on the McMaster-Carr website or representative, so I can tell anything from those.

Again, I'm positive these screws are nothing special. The equipment is electronic, used inside, and under no physical stress.

IMG_3491.jpg
 

ste6168

Mike
Senior User
Zinc plated on the top, stainless on the bottom, maybe? Don't know for sure, the one on the bottom looks a bit shinier than the stainless I am used to seeing.

Interesting question, look forward to seeing others thoughts.
 

Dave Richards

Dave
Senior User
I'm thinking the same as ste6168. Although not definitive, try picking them up with a refrigerator magnet. The stainless one will either not be attracted to the magnet or only weakly attracted depending on the grade of stainless. Might that the screw was used where it was because of the need to avoid magnetized screws or maybe to avoid galvanic reaction?
 

blackhawk

Brad
Corporate Member
They could both be zinc plated. There are several types of zinc plating. Even the same zinc process can have color variations from batch to batch.
 

Oka

Oka
Corporate Member
If you heat them to say 600 to 700 degrees then take a little piece of leather soaked in linseed oil you can darken them, if you go to hot it will turn blue, just get un-plated, stainless or cad coated
 

cobraguy

Clay
Corporate Member
+1 for the zinc on top and stainless on bottom. I have some of each from McMaster and that color difference is exactly what I see.
 

Pop Golden

Pop
Corporate Member
McFeelys catalog has a complete color chart. In the reproduction world Horton Brass has the real creations of the old stuff, but bring money. Maybe like a Brinks truck.

Pop
 

Rick Mainhart

Rick
User
They both appear to be zinc plated. The top one was post-plating treated with a blue chromate bath, the bottom one was post-plating treated with a yellow chromate bath.

I worked in a chrome and zinc plating plant right after high school, and we had both yellow and blue chromate on the line ... we'd use one until the tank needed a rest, and would switch to the other ... though typically not in the middle of a job. Some customers requested a particular chromate finish and we'd schedule their jobs when that color tank was on-line.

Hope this helps,

Rick

I do some equipment restoration as a hobby. Looks are important. Take a look at these two screws. One is shiny silver, the other is darker.
 

Hmerkle

Administrator
Hank
Mike,
Rick is correct - the top one is zinc and clear chromate or zinc and blue chromate and the bottom one is zinc and yellow chromate.

The zinc is the base coat applied to the fastener and the chromate coating is applied to keep the zinc from corroding.
Nearly everyone uses Tri-valent coating now as Hexavalent is nearly banned around the globe.
While the hexavalent coating was better as a corrosion barrier, it is harmful to the environment and a known carcinogen.

As you mention these are likely the cheapest fasteners available (McMaster Carr, Lowes, etc.) are manufactured in China or another low-cost country (India, Vietnam etc.) and hence the "coating" is as cheap and fast as they can make it...

The thickness of the coating is the factor in maintaining a corrosion-free part. Since this is an indoor application, you really don't have to worry about corrosion unless you are in a humid environment.

I will stop now as the presentation I give on fastener coatings can take 1 to 4 hours depending on the student's desire...
 

patlaw

Mike
Corporate Member
Mike,
Rick is correct - the top one is zinc and clear chromate or zinc and blue chromate and the bottom one is zinc and yellow chromate.

The zinc is the base coat applied to the fastener and the chromate coating is applied to keep the zinc from corroding.
Nearly everyone uses Tri-valent coating now as Hexavalent is nearly banned around the globe.
While the hexavalent coating was better as a corrosion barrier, it is harmful to the environment and a known carcinogen.

As you mention these are likely the cheapest fasteners available (McMaster Carr, Lowes, etc.) are manufactured in China or another low-cost country (India, Vietnam etc.) and hence the "coating" is as cheap and fast as they can make it...

The thickness of the coating is the factor in maintaining a corrosion-free part. Since this is an indoor application, you really don't have to worry about corrosion unless you are in a humid environment.

I will stop now as the presentation I give on fastener coatings can take 1 to 4 hours depending on the student's desire...
All of the information in the thread is very helpful, but I'm still not sure that the these old screws were shiny when new. Maybe I'll send you one of the old ones to evaluate, Hank.
 

Hmerkle

Administrator
Hank
They both appear shiny in the picture, so you must have something "shiny-ier" that you are comparing them to or notion in your head of what they "should" look like...???

If you have nickel plated screws (think the silver terminal on an outlet) or passivated stainless - they might appear more shiny.

From you picture (and that can be deceiving) the top one appears to be a zinc and clear chromate finish and the bottom one appears to be a zinc an yellow chromate finish...

Still, happy to evaluate.

The real question - what do you want? or what finish are you wanting to use?
 

nn4jw

Jim
Senior User
Mike, did you try a magnet with the lower pictured screw? That would certainly be a good test to rule out stainless and take all of 10 seconds.
 

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