The patination of steel is actually a form of ‘controlled corrosion’. The patina color/s are subject to fast deterioration, darkening & rusting & because of that, must be clear-coated.
The clear-coating will preserve not only the steel, but the colors that you have achieved with the patinas and/or dyes.
Properly clear-coating an outdoor, patinated piece will give it a 15-20 year life-span, possibly more. In answer to your question, all patinated steel has to be properly clear-coated as that coating is what gives longevity to the doors or railings you mentioned.
For pieces that are to be displayed indoors, you can get by with oil, wax or a single-stage clear (rattle can) aerosol from any hardware store. Rustoleum & Krylon are the leading brands. Not so great for an art piece or high-end piece that needs a deeper film thickness and “dipped in glass” look. That’s why I use a 2-stage clear, which is an automotive finish, as it has no equal in appearance, UV protection and longevity.
I would encourage you to watch all of the videos on this site HERE and have a look at the eBook, which I will attach to this email at no charge. Write down your questions & email me or call me at 1-800-710-1273.
There’s some pretty good info in my eBook, ‘Steel Patinas & Finishes’ that may help.
And, if you’ll review some or all of the videos on the website, and my YouTube Channel…you’ll see all of the basics & some intermediate and advanced techniques, as well.
The whole process of colorizing steel, either with patinas or dyes, is really very, very easy. And it’s the single most important thing you can do to increase the value of your work.
Let me know if you have any questions.
Thanks!
Bill
p.s. – I can be hard to get on the phone some days, so email is probably best for starters. The 2nd Edition of the eBook, which will include a LOT more info, is due out in the Fall of 2018.
If you’ve read this Q & A this far, and don’t already have my eBook, ‘Steel Patinas & Finishes’, you’re in luck! You can download it,