What's the best method to clean an old porcelain tub?

See if this helps!

https://m.wikihow.com/Clean-a-Porcelain-Tub

Many people use abrasive products and scrub too vigorously which in turn ruins the finish. You can always have the tub reglazed. I have done it a number of times.

1. Hi Paula!
2. Soak a non-abrasive sponge in the baking soda/ammonia solution. Scrub the surface of your porcelain bathtub or sink, paying particular attention to stained areas.
3. You can even make a paste out of this and leave it to sit on the stained or hard to clean areas.
4. Dip the sponge (make sure it's a soft sponge) in the solution, scrub and repeat until you're satisfied.
5. Rinse well.

After rinsing, wipe thoroughly with a clean rag or the baking soda will leave a white film behind. Hope this helps you!

Here are various methods to try:

https://www.apartmenttherapy.com/how-to-clean-an-old-porcelain-enamel-bathtub-or-sink-137148

https://home.howstuffworks.com/home-improvement/household-hints-tips/cleaning-organizing/clean-old-porcelain-tub.htm

https://www.wikihow.com/Clean-a-Porcelain-Tub

https://www.apartmenttherapy.com/how-to-clean-an-old-porcelain-enamel-bathtub-or-sink-137148

Bartender's Friend is an amazing powdered cleaner. I hope you'll give it a try.

Kohler Cast Iron Sink Cleaner. I bought it at Amazon and it did a great job on my tub when nothing else I tried cleaned it.

l have been amazed at how well Barkeepers Friend works in these applications. Cheap too!