gunmetal or brass?


I have a 2-part question re gunmetal tools (specifically British infill planes).
First, about evaluation.  Given two otherwise identical planes -- one brass the other gunmetal --  is one more valuable, and by approx. how much??
2nd, how do you tell the difference between the two? [I know gunmetal has less tin in the alloy.] Side-by-side (which is almost never) gunmetal  usually looks lighter in color, but....   Any hints? Thanks

My understanding is that what the British call gunmetal is a particular alloy of bronze.  That is it's copper and tin.  Brass is copper and zinc.  Depending upon the percentages of the metals involved, as well as any additional elements in the mix, it is not really possible to distinguish the two metals based on a visual examination alone.  Though some people claim to be able to do so.  I suppose they have spectroscopic vision.  Most of us rely on  descriptions of the tools by their makers in order to state what metal they are made of.  Catalog descriptions by Spiers, Norris, Matheison, etc. all indicate that they use gunmetal bodies and parts.  There were many craftsman made planes that could have used brass.  I am generally of the belief, based on no evidence or experience other than hearsay, that brass tends to be more brittle than bronze.  This may simply be a matter of the alloys used.  If this is true, however, it would make the plane more vulnerable to damage, and so a little less valuable.  But, consider all the cast iron planes there are out there and how vulnerable they are.  Given all the factors to be considered in buying an old tool, I consider the alloy of which it is made to be minor.  But, if you want to be safe, buy one by a known maker.  And remember, the best ones have steel soles.  PSP
Thanks Peter.  I'm a (minor) collector and a price guide I often refer to lumps certain planes into steel/iron vs copper/gunmetal; the latter being more valuable all else being equal but not saying whether a copper or a gunmetal one
is pricier when confronting that choice.  Sounds like perhaps the gunmetal.