Washing the skin of a dead rat

There is an idiom in Indian languages :

There is no use washing the skin of a dead rat for even a year

The idiom means a foolish person or thing can not become useful even if we try to mend them for a long time

I would like to have an almost equal idiom in English

It is not a duplicate because the idiom considers to be equivalent to be mine does not even nearly mean the same.The meaning is totally different.

Washing the skin of a dead rat means trying to make something good for too long when the thing brought for mending is useless even in the begenning.It was really foolish to start it and continue to make it useful all the more foolish.

A very old saying comes to mind: "you can't make a silk purse out of a sow's ear" meaning it's very difficult to make a fine article out of inadequate material, or it's impossible to train a very stupid person to become the owner of a brilliant mind.

• One cannot turn something inherently inferior into something of value. This proverbial metaphor dates from about 1500, and with some slight variation (“silk” is sometimes “velvet”) makes its way from proverb collections (by Howell, Ray, Dykes, et al.) into literature (Samuel Richardson, Laurence Sterne, Jonathan Swift, Charles Lamb, Robert Browning, George Bernard Shaw, and Clifford Odets, among others). TFD

A somewhat crude but memorable equivalent is:

"You can't polish a turd."

It also gives an idea of what the result would be if you could do it.

"Lipstick on a pig."

is a similar expression, but typically used in different situations, where you can do it.

The "polish" idiom is usually said when someone suggests or is about to do something that will be a waste of time. (In design, this would be when someone suggests making improvements to something that is already so fundamentally bad that it should be discarded.)

The "lipstick" idiom is usually said after something has already been improved, made to look more attractive even though what's underneath the makeup remains just as ugly as it ever was. (In marketing, this would when someone repackages the same useless product in order to increase sales.)