Murf425
One of the neat things about building your own rifle or pistol from a kit is it can be whatever you want it to be.
Everyone has their own little likes and dislikes but you don't have to please anyone except yourself.
I'll give you some of my thoughts on the options for finishing metal:
"In the White", that is, polished bare metal.
This option is usually not liked by hunters because of the shine. If you choose to do this, remember that if the surfaces are just sanded they will show finger prints and rust fairly quickly.
If they are truly polished to a mirror shine they are much less prone to rust.
"Antiqued": In this case meaning the appearance of an old, well used "In the White" finish. It is usually a soft grayish color and can be done using things like mustard, Naval Jelly, and some other mild acids.
Blued: Fitting for 19th century guns there are two ways of doing this.
Cold Bluing: Usually made for "touch up" finishes it can look quite good or rather mottled.
Cold Instant Bluing is not very durable, the sharp edges being the first to show wear.
Cold rust bluing: This process is basically a Browning process using a rust browning method. The hard brown rust is then treated to a bath of boiling hot pure water which turns it black or blue/black.
This form of bluing is very hard and durable.
Heat Bluing: Good for small parts where the part is heated until it turns blue and then dropped into some oil to cool it. This is not a durable finish.
Larger parts like a gun barrel are rather difficult for the average person to blue at home.
Hot tank bluing: Way beyond most home builders capabilities because it deals with melted "salts".
This type of bluing is quite durable but having it done by a gunsmith is costly.
Browning: There are two methods for browning, one hot and the other cold.
The hot method uses Birchwood Casey Plum Brown.
The parts must be heated to 275 degrees +/- 10 degrees F. for it to work. This can be done in an oven or with another source of heat like a propane torch.
When the solution is applied it acts instantly. It usually takes several applications to get an even looking coat.
This method is very shallow and leaves the appearance of the metal unchanged so if the surface is shiny it will remain shiny.
It is fairly durable, much more than the Instant bluing that was mentioned above.
The fumes are rather nasty. It should be done outside.
The cold method is done by applying a non-toxic solution to the part and then subjecting it to a humid environment where the surface rusts.
The rust formed is a very hard dark brown rust that is very durable. (This is the same method that was mentioned above under bluing.)
Several "rustings" are required to get a good even finish.
This finish actually rusts the surface so the finished coating has a soft velvety non reflective look.
Because many feel that some of the original guns made in the 17th century were finished this way, and many of those guns, even if finished "In the White" or blued have naturally browned over the past 200 years, is the preferred finish for most muzzleloaders.
It is easy to do, very durable and it looks authentic.
There are some other methods but this should give you a good idea of what is available.