I don't think the barrels were left long enough with the rusting agent on them. They should have turned to an orange rust color. This time of the year is tough to rust barrels as there is not enough humidity.
You didn't say if the barrels were in a rusting box or not, but if not you will need to either build one or use a large clear plastic bag with a bowl of water with the barrels suspended and close the bag and wait for that orange color to appear.
By now after 14 rustings you should have had a decent color.
