Iwachu Hobnail cast iron teapot (kyusu)

This cast iron kyusu made by Iwachu is about 7" wide including the spout, 5.5" in diameter and about 3.5" high, not including the lid. It has the Heisei (?) Iwachu mark and "Made in Japan" on the bottom. It weighs 3 lbs 10 ounces and the lid, alone, weighs in at 9 ounces and is vented by a groove in the underside of the lid, which fits very loosely. It is very heavy for its size, much heavier than the two other Iwachu kyusu which I posted recently. The capacity is about about twice that of my other Iwachu teapots (kyushu). It was probably made for both domestic sale and export due to the "Made in Japan" on the bottom. Iwachu calls this pattern "Hobnail", or in Japanese "Arare".

The video at the link below explains Iwachu as a company and shows how a tetsubin (kettle) is made:

https://www.youtube.com/watch?v=o6AuxztRkYM

At first, I thought this was a tetsubin (kettle) due to its size, the lack of a vent hole in the lid and the seller's images which seemed to indicate that the interior was un-plated and rusty. When I received it, I was surprised to find that the interior was plated and not at all rusty, but in perfect condition. It is, however, heavily stained by whatever tea was brewed in it, apparently through many brewing events. I wiped the inside down several times with a damp paper towel and got a lot of tea stain on the towel but could not get it to shine, though after a couple of towels no further discoloration was removed. This is probably exactly what would be desirable if only one type of tea would ever be brewed in this pot. I can't really taste tea, so I will probably just leave it alone and not try to restore the inside any further.

It has been pretty gently used but was not properly cared for and has rust and wear to the bottom which cleaned up quite a bit with just a bit of rubbing with my bare fingers. I will be cleaning it up to remove the rust and will have to do some research to see how to do that to get a correct finish back on it. I have a lot of cast iron cookware, but guessing that the process used to clean and re-season that will not be appropriate for a Japanese kyusu. My initial reading suggests that just rubbing the outside with a tea dampened cloth is typically used to maintain the exterior finish. Any input on that is welcome.

https://www.sensationalteas.com/use--care-tetsubin-kettles.html#/

I have been keeping my eye out for a tetsubin and had hoped to find an Iwachu kettle with the old mark to match my first two kyushu but this piece was very inexpensive, appeared to be a tetsubin and screamed for some TLC so I picked it up. It was literally the least expensive Iwachu pot I could find and I was really disappointed to find it is not a tetsubin but very pleased to add another nice kyusu to my collection. The seller did not realize it was made by Iwachu so I paid about one tenth the cost of a new kuysu for it. The seller's images also made it look like the outside of the pot had a lot of rust but it is not rusty at all. I will keep looking for a Showa period kettle but happy enough for now.

Some really good information about how boiling water in a tetsubin changes the water to make it great for brewing tea. The link also contains some great information about making and using a tetsubin some of which also applies to kyusu.

https://hojotea.com/categ_e/tetsubin.htm

This link contains a good explanation of the difference between tetsubin and kyusu.

https://en.wikipedia.org/wiki/Tetsubin