St Andrew's Cross, also called Crux Decussata
This is a painting of the Martyrdom of St Andrew, i.e.Saint Andrew being tortured on a saltire cross, now called a St Andrews Cross.
For more information about Saint Andrew, read en.wikipedia.org/wiki/Saint_Andrew
This painting is exposed at the Casa Nacional de Moneda museum in Potosí (Bolivia). If you know its origin or have more information, please post a comment or email me.