I am interested if anyone has thoughts about the case coloring on this Fox. It is a 12 GA CE grade made (I believe) in 1909. It appears to have been refinished but the case coloring is quite yellow, any ideas what causes this? Thanks for your help!

Varnish or oil top coating can do that. I can’t see the gun clear enough to decide if that is what it is.

Best,
Ted

The colors that result from the case coloring process appear to be highly variable. It seems that the colors are the result of many different factors including the composition of the charcoal, temperature, the quench, the amount of air the parts are exposed to during dumping the contents of the crucible into the quench, aeration of the quench, the composition of the steel, etc. Most practitioners seem to get fairly consistent colors once they settle on a process using the same techniques and materials. Since many people who do color case hardening well are rather secretive about their process, it is not easy to say definitively what caused those particular colors on your gun. But whoever did it sure got very complete coverage.

if you dont like it and it is not dried oil and/or varnish...prep with alcohol and try cold blue on a qtip, in a hidden area...if that looks good to you, then continya...or do nothing...

Oxidized oil comes off with a solvent
Sometimes guns turn brown with it
But a golden patina seems to always come from the pack
It is in the surface not on it

See what some nail polish remover and a tip does under the forend

Is it possible to remove varnish buildup without affecting case coloring? What solvent to use?

A non polar solvent will remove oils, varnishes, shellacs, lacquers, (all at different rates) without dissolving the metal oxides that make up case coloring.
Don't scrub.

You can rank their aggressiveness by volatility.
Hotter solvents evaporate faster.
So, acetone, ether, mek, lacquer thinner, xylol, pentane, hexane, heptane, petroleum distillates.

If you dab some on under the forend, and nothing lifts to a swab, it's the oxidation of the metal surface, not oxidized oils.

Off to the races.

Pretty sure that's just a bad job of case coloring. Bad pack, wrong mixture, too much heat, too little heat, quenched wrong, whatever.
JR

Agreed.

If you look at enough heat treated parts, you’ll see that bronzing on occasion.

In production, it turns out that the wrong alloy was used when the parts were made.

Every so often, somebody that is coloring parts runs into a problem like this, usually a quality control matter in their preparation of their pack, I don’t recall ever seeing any evidence that said it was from the impurities in the rain barrel. Bubble size yes, but not impurities in the water.

It is an interesting receiver to look over in the pictures. How ever the effect was achieved, maybe the heat was on the low side for quenching? There is little differentiating of colors between thick and thin areas, pin holes, etc.?

Pretty regularly, gray/black is passed of as case color background, so maybe the effect isn't so bad. I would guess the hope might have been to work more blue color in, and get that deep purple burgundy fade. In any event, there seems to have been some intention, and maybe a pro would have just redone it if it was not perceived as pleasing?

Every shop I’ve ever worked with could show you what their work would end up looking like. They were quite proud of that.

I think on occasion here, we see barrels that have been refinished, that end up with bronzing, because some alloys just don’t take browning solution the same way as others.

It can be quite frustrating to the barrel refinisher

What does it look like in the hidden spots, i.e. watertable, bottom of forend iron? Same bronze?

If you hot blue a color cased part it will come out oddly colored.

Thanks for all of your input. The finish looks uniformly bronze including watertable and forend iron. I don't dislike it I was just wondering about it since I hadn't ever seen anything similar. I will try some solvent in one of the hidden areas and see if anything changes.

You might also try a file in a hidden location and see if it particularly hard as it would be if case colored.

Someone correct me if I'm wrong, but I believe today at least, there are two different ways of coloring a receiver. One is "color case hardening", and the other is just " case coloring " . How the second is done, I'm not sure of. My friend uses bluing and browning solutions, bluing solutions cut in half with water, and so on. He doesn't clean the receiver, and dabs it on with his finger, wipes it dry when he gets the color he wants. Sometimes depending on the amount the steel is still hard he gets very good results. Other times not so. This I believe is not what I was trying to describe in the beginning.