There are two common ways to accelerate the rusting and patina process for Corten Steel Planters. First method is to use muriatic acid and the second method is to use a mixture of peroxide, vinegar and salt. With both of these methods you want to make sure you are wearing goggles and rubber gloves. Also, make sure the accelerant solutions are applied outdoors in a well ventilated area and the planters are placed on grass or other surfaces that will not stain with rust run-off. It is important to note that accelerating the rust / patina on Corten Steel Planters is only an aesthetic step and will not seal the metal or prevent future rust run-off.
To accelerate the patina on Corten Steel Planters dilute muriatic acid with water to 50/50 ratio of water to acid. Generously apply the acid solution onto planters with a brush. Allow the mixture to react and dry for 2 hours before spraying with water to reactivate the oxidation process (repeat this step two to three times based on desired appearance). WARNING: Use Only 10% Muriatic Acid Concentrate. Read all printed instructions for usage of the Muriatic Acid on the bottle or packaging. Only use Muriatic Acid as directed by the manufacturers. Children should not handle Muriatic Acid.
To accelerate the patina on Corten Steel Planters using peroxide, vinegar salt solution dilute 16 oz of hydrogen peroxide, 2 oz of vinegar and ½ table spoon of salt. Spray the solution onto the planter allowing time to dry between each application.
The peroxide, vinegar salt solution takes considerably more time and effort than the muriatic acid approach. Muriatic acid is more effective at cleaning the Corten Steel and etching that steel to form a stable rust layer. Please see the video below for a comparison of the two processes.