If you wash your cast iron with eg Dawn dish soap, you can definitely clean it down to bare metal and it will rust. I usually will clean the cast iron pan last and use the sponge that just has a small amount of soap left in it. Just watch it as you clean, if the shiny hard coating seems to be going away, rinse out the soap and make something greasy next time you use the pan to replenish it.
If you wash your cast iron with eg Dawn dish soap, you can definitely clean it down to bare metal and it will rust. I usually will clean the cast iron pan last and use the sponge that just has a small amount of soap left in it. Just watch it as you clean, if the shiny hard coating seems to be going away, rinse out the soap and make something greasy next time you use the pan to replenish it.