Vintage Woodworking Chisels

Greetings all, I took home a handful of bench chisels to restore and use but have a question for those of you with more experience with this tool.
My question is, for the first chisel pictured below, the backside is no where near flat. I wanted to know whether I should be prepared to hone or down until the entire back face is perfectly flat or if it's okay to just flatten the last inch or so closest to the sharp edge (which is what it looks like was done to this one).
The other pictures are examples of ones from the same haul that were much flatter overall.
https://i.imgur.com/rSMFFOy.jpg
https://i.imgur.com/TB0nUdt.jpg
https://i.imgur.com/KNyRhzg.jpg

Cheers!

Don't think you need to flatten the whole thing, just the part by the edge. In fact unless the back is pitted by the edge i don't see any reason to do much polishing/flattening. I would think that a little upsweep like you have is desirable for times when you need to lay the blade on it's back for certain cuts. JMHO

Old timers like Paul Sellers, Chris Schwarz (he's not that old...), and others recommend "initializing" all plane irons and chisel blades by first flattening and polishing the back to just a sixteenth or eighth inch out from the cutting edge. This will facilitate creating a wire burr when honing the bevel edge. Finishing on a bench strop with a fine cutting paste will give you a razor sharp edge that will allow you to easily pare White Oak end grain. After that you could create a micro-bevel on the back using the "Ruler Trick" but that is usually only for plane irons, not chisels.

Sometimes you will get a blade that has an uneven or concave back that will require quite a bit of work on diamond hones, or wet dry sand paper, or both to get to that 16th of an inch. Those can be a pain, but once done it is worth it.

By the way, that curve to your chisel might only be a problem if you need to use the back of the chisel to reference a surface such as when paring out dovetails, or other detail work in which case you want a chisel that has a dead flat body. You could still use it to roughly chop out a mortise, scrape glue, and open cans of paint.

In theory the back of a chisel should be dead flat, for paring and using the back as a guide.

But in reality, one almost never lays a chisel fully flat on a surface or the piece to be paired and it is usually less than an inch.

Your chisel may have been flatter when new, but years of sharpening, probably on aggressive silicone carbide stones have worn the back slightly out of flat. It is normal to put more pressure on the tip near the bevel.

Some flat carving chisels are ground on both sides because they are never used with the back flat on the work surface.

The bottom line is it does not matter. Look at the thousands of videos of guys cutting dove tails and tenons and you will almost never see them lay the chisel back flat on the work or the work face is very short.

Old tool carbon steel seems to like an edge from a Washita Arks stone. You can still find them in the wild. You do not need a large stone, 6x2 is plenty, but large is nice. I use a 140-diamond plate from CNTG and finish on a Washita, or straight to the Washita off the grinder.

One of the best explanations I've heard:

https://www.youtube.com/watch?v=5yj16u7udlw

More great advice on chisels:

https://paulsellers.com/knowledge-base/chisel-advice/