do milling marks typically denote a more recent piece of iron?
It depends on what you call recent. From 1880 to 1980, roughly, many griddles as well as other cast iron cookware, were ground smooth. After Griswold and Wagner were bought up and phased out by new owners in the late 1950's and ‘60's, foundries like BSR and Lodge continued to finish cooking surfaces on skillets and griddles until the machinery wore out and replacement parts were no longer obtainable. BSR and Lodge sold both plain and finished versions of their cast iron products throughout their history. So both ground and unground griddles have been made throughout the history of cast iron. Before the late 1800's, you can find the smooth, gate marked castings that period is known for. If you are looking for one of these round griddles, don’t forget to make sure they sit flat. They were made to sit in an open stove eye, but on a newer stove like a glass top or induction surface, these griddles might not sit quite flat due to the bottom gate mark. All current era cast iron round griddles, like the Lodge 9OG, are not ground smooth. They have Lodge’s pebbled texture, which people either seem to love or hate.
Milling is a different process than that which produced the ground smooth surface common on vintage cast iron, and milling was only used sporadically by foundries in the past. Some new boutique foundries may also perform this type of surface modification to create smooth surfaces on their new products.
Do you want to use a round griddle to simply heat tortillas, or are you making them from scratch and cooking them on a griddle?
For the tomatoes and peppers, I would recommend broiling them in the oven to blister them. I use a new Lodge LJSCP3 Jumbo Chef's platter Cast Iron Rectangular Griddle 15" x 12.25".
https://www.lodgemfg.com/bakeware/cast-iron-rectangular-griddle-15-by-12-25.aspI use both vintage and new cast iron griddles when making tortillas from scratch. Instead of a round griddle, I find it more productive to use a new Lodge long griddle or a Lodge pizza pan; since, they both hold more than one piece of bread. When making crepes, I use an old gate marked #8 round griddle. It the perfect size, and they are the lightest in weight. It is very easy to flip the crepes in the air to turn them. Look for one with sloped sides, not straight, shallow sides.
In my second cast iron cookbook, The Quick And The Bread, I show how to make 13 types of quick bread and flatbread. You can view/read/download about the first third of the book for free. That part actually covers making both corn and flour tortillas. There is also an Appendix in the back of the book that details all of the cast iron cookware used in the book.
Here is the link to the book/sample if you are interested:
https://www.amazon.com/dp/1523655496
