  In an effort to obtain further observational evidences for secular evolution
processes in galaxies, as well as observational constraints to current
theoretical models of secular evolution, we have used BVRI and Ks images of a
sample of 18 barred galaxies to measure the lengths and colours of bars, create
colour maps and estimate global colour gradients. In addition, applying a
method we developed in a previous article, we could distinguish for 7 galaxies
in our sample those whose bars have been recently formed from the ones with
already evolved bars. We estimated an average difference in the optical colours
between young and evolved bars that may be translated to an age difference of
the order of 10 Gyr, meaning that bars may be long standing structures.
Moreover, our results show that, on average, evolved bars are longer than young
bars. This seems to indicate that, during its evolution, a bar grows longer by
capturing stars from the disk, in agreement with recent numerical and
analytical results.
