Update: I very much agree, AAAndrew!
I have managed to get the Mitchell nibs to work fairly reliably; in fact, they work just fine with no reservoir on them at all, so the problem is obviously in the placement/adjustment of the reservoirs.
I can verify that as has been pointed out, the linear adjustment of the rez is critical to ink flow: closer to the edge yields greater flow, further back towards the heel reduces flow. Perhaps the most critical adjustment though is how firmly the side-prongs of the rez are squeezing the nib; I've found that even if the nib looks flat across and appears to be in no 'distress,' they can still be very hard to start.
I noticed the tabs are twisted, so that the forward edge of the tab is further inward than the trailing edge is; straightening out that twist (so the tabs are parallel to each other and not converging, like the sides of a cone would be) and then adjusting the 'squeeze' so that they just barely hang on seems to be the ticket. They do stay put, but require very little effort to slide back and forth on the nib. A little 'scrub' is still often needed to get them started... I just do it al the time now. I also find that it's best to 'blot' the nib after dipping/shaking/dragging it across the ink-holder lip by drawing a short line or two on some scrap paper before addressing the work; I get much sharper letters and less ink 'pile-up' on the first letter. I don't seem to be having a lot of luck in finding a decent too-much/too-little balance using a brush to load the nib's underside... those darned Mitchells again!
I don't have a similar issue using the same or different inks on other nibs; the Mitchells remain cantankerous.
They are worth the effort, though! Once the reservoir is adjusted to my liking, it doesn't have to be messed with any more, so I just view it as a required 'set-up' step before actual use, a 'one-time' procedure to get things rolling, then a little forward or backward slide to accommodate the characteristics of whatever ink/paper is in use. That particular reservoir then takes up permanent residence on
that nib only. Lots of things have to be set up prior to use, and these nibs are no different. I now quite understand that 'live' feel that some use to describe them; they are 'bouncy' and give great feedback... the Tachikawa's (previously my 'go-to' broad nibs) feel numb and dead now in comparison, like the difference between a flexible nib and a 'nail' nib on a fountain pen.
Thanks for the info on the heat-treat as being the source of the nib's color. That's kind of what I was looking for initially... bronze or some other coating or treatment? In some of the pics I've seen of these nibs in use, they don't look like they do in person, they look more like silver than brown-ish, so I wondered it the color was some really stubborn coating that had to go. I've seen metal of all colors across the spectrum from heat-treatment, so this is not a surprise.
And thank-you all for the great information and suggestions that opened these things up to me! Couldn't have done it without you, I"d have given it up and stuck with something else, to my own loss.
