the Old American Foundries Sold Their Doorstops :
2. UNPAINTED (Black)
3. ELECTROPLATED with Brass, Copper or Nickel
UnPainted: You could paint the doorstop yourself with a kit (paint & instructions)
The Albany Foundry even went so far as to supply
instructions on the cover of their 1926 catalog.
To see those Original Painting Instructions
First, a base coat was applied to the entire casting
Usually, this base coat was white. But, some foundries used a different color.
The only Purpose of this overcoat was: to protect the cast iron from Rusting
Today, we know this process as using a primer coat on the metal.
    --- Judd usually used a Brown or Green.
    --- Hubley usually used a White.

Second, the front of the doorstop was painted in various colors.
They used tubes of oil paint or enamel (if a shiny surface was desired).
Each different color was applied & allowed to dry.

Thus, viewing a factory painted doorstop where its color has woren off,
you should be able to see its base coat color underneath.

Hubley's Fish doorstops were specially finished to achieve a "high gloss".

Electroplated Electroplating creates one solid color.
(The painted version with all its colors
is prettier and much more desireable)
Values are drasticly affected by the different ways a doorstop is finished:
Black / Unpainted - have practically no value
Electroplated - are not desirable with very minimum value
Painted in Colors - the most desirable & what the values are based on at this website

    Ways to Determine Re-Painting      

A Difference in the Shade of Color
This should be the most obvisous to discover.
Using pictures of the original doorstop at this site,
its shade of colors should match
the colors on the doorstop in question.
For instance, the red color on Hubley's doorstops made by Fish,
is the same shade of red for all 7 Fish doorstops

Beware of Shiney Paint
If the paint is real shinney, it is a possiblely because
it is new and not a hundred years old.
This doorstop is likely to be a Reproduction or has been Repainted.
Repainting destroys the value of the doorstop

Compare the Condition of the Front with the Back
If the paint is in great condition on the front
and the back is a disaster (in bad shape).
Then, you know the front & back have not aged properly together,
signifing a possible a repaint.

Spray Painting:
In 1892, Francis Davis Millet is generally credited with the invention of spray painting.
So, spray painting did exist during the Doorstop Era
Probably, its only use would have been to apply the overall base coat.
The Front of Original Doorstops had to be hand painted due to all the intricate features.

Inspect for a Smooth Continuous Surface
At the interface of the paint and where the paint is missing, there is a ledge
where the surface of the paint steps down to the unpainted area.
Ever so slight, it is may be able to feel this ridge with your fingernail..

When repainted, the paint goes over both where the paint is missing,
and the original paint. It would be impossible to accurately paint
just the bare spots and not have some paint go onto the original paint.
The point -- paint over each of these areas looks different.

This "Color Difference" is best illustrated in the example below:

Note the cream color of paint on the legs
There 2 distinct areas
Dark & Soild Cream

The Dark Area is the repainting
over an UpPainted area
The solid cream is over the Original Paint

In another example:
Note - the breaks in the paint surface
especially along nose and on the chin
showing clearly this as a repaint.