We were fortunate to have been given a few old large tin cans from a local cafe with the idea of transforming them into great, affordable planters. We brought them home, made sure they were completely clean and then took them outside in the fresh air. We first gave them a spray coat of metal primer and once this was dry, gave them one coat of white Hammerite metal spray paint. We've transformed several around the home but equally they look great unpainted. One word of advice, make sure they're grease free as if not, the paint won't stick. Also, be a bit careful with the top edge as it might be a bit sharp.
We've just popped some plants straight in and we love them. *You could do these with any size tins, they needn't be the large ones shown here.