Dear Fjon,

You could try chemical etching. If the sample is polycrystalline in nature, some of the crystallites will be preferentially eroded, faster than others. You could passivate the surface later, when desired porosity has been achieved.

I hope it helps

Hi Aditya,

Yes, chemical etching is what I want to do, but the details are what I need to learn. Do you know how to do the chemical etching? chemicals? percentage? temp? time?

Thanks

you can check the publications from DR. Lluis F. Marsal, he has done much work on porous anodized alumina.