have dmt diamond stones that range from bumpy concrete all the way up to 8k. I also have some naniwa stones ranging from 1k-12k.
sounds like you dint need to buy anything more from stones to razors right now.
My noob thoughts are that if I assume my DMT stone is flat (I have not checked it) and I have a good bevel on one side but no contact in the middle of the other the spine or the edge on that side is not planar. I suppose the next step is to put it on a flat plate and test it with a thin feeler (or shim)? Or should I measure the spine thickness? I don't have a micrometer (only some calipers) but I might be able to borrow a reasonable one for an afternoon.
sounds like it may be warped. Id focus on the ZY and get that thing shaving well. Its a known commodity as is the sheffield. The crystal maybe ok ¯\_(ツ)_/¯ could be an RSO, someone else might know better. Might be made in the next neighboring factory to the zy.
try going horizontally with the marker instead of vertical, doesnt make a difference other than time and coverage. I wouldnt measure anything yet. Thats not a huge deal for this.
i would assume the dmts are more or less flat enough. Are they the 8x3 or 6x2ish? Assuming the zys are similar to the better gold dollars, You should be able to get the bevel set on ~1Ks dmt or synth (check flatness on the synths using the pencil grid lapping on a 600ish dmt).
i have tried the burr method, it works but if you feel it isnt working for you
work each side evenly, laps, circles, back and forth and keep checking the edge often using one of the tests. There should be a bit of pressure on that zy... not a ton but enough. the chinese blades may have some more grind issue than the vintage English blade you have.
once you get that edge set, jump to 3k-5k. not so much pressure and try to feel the transition. Probably around 25 laps depending on your pressure, stone and razor. Then 8k same deal maybe 15 laps, the 12k 10 easy laps. But definitely dont move on from bevel until its 100% set.
As you learn you may want to very very gently apply pressure equally along the spine until you get the feel for what you are doing at each portion of the edge and you experiment with different technique.
Use the marker a lot. Its not a crutch, its a tool.