is diluted with......?
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That depends on what you're starting with, which was usually the
residue of earlier work, saved specifically for this sort of job.
Most often, you'd start with stuff already thinned for spraying, use
whatever thinner or reducer was used on the original batch. The
objective was to produce about a quart of water-thin mixture, most of
which ends up on the rag or glove (you squeeze harder when the 'wipe'
starts thinning out).

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1:1?
1:3?
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Normal use for liquid ZC is 1:1 with reducer, which you then fine-tune
according to the type of gun you're using. At a guess, that would be
further thinned by about 1:1 for wiping.

Starting with paste, using mineral spirits, it's probably on the order
of 6:1.

The whole idea here is to use what's already at hand, and to produce a
finish that is as easy to REMOVE as it is to apply because it wasn't
economically practical to produce just one fully-finished airframe at
a time. Instead, they were produced in small batches. In the serial
production of airframes, a lot of shops had only one 'finish' weldor
and space for only one airframe. (Back then, you made your own
acetylene and most welding was done near the generator.) Once the
basic airframe was 'on the gear' (which was often just a cart or pair
of dolly-wheels), it would usually get gloved and stood on its nose...
or moved outside the welding area. When it came time to add all the
tangs, clips, brackets & fittings, an airframe was returned to the
shop, the areas on the airframe that were to receive new weldments
were wiped down to remove the ZC and the parts positioned using jigs
that attached to the airframe. It sounds pretty low-tech and it was,
but some famous shops operated that way for 20 years or more.

Cosmoline and other wax- or grease-based surfactants were normally
reserved for MACHINED surfaces, like axles or weapons -- parts that
would not normally receive paint in any case.

-R.S.Hoover

PS -- Some shops didn't use zinc chromate on steel, preferring to use
various anti-corrosion paint commonly referred to as 'red lead.' Same
general rules applied: thin coat wiped on for temporary storage,
final coat sprayed-on then sealed with varnish or paint.