Jay, my quoted times are based on working with traditional hand tools, not electric tools. I do not know of anybody today who uses the traditional tools. Electric tools are very much faster.
In Australia I used coke, coke is produced by industrial processes from coal. There are various types of coal & various types of coke. The coke I used came from Corrimal Coke works, and was mined in the Illawarra district of NSW, Australia.
When I was learning blacksmithing from Gordon Blackwell, who was very probably the last traditionally trained blacksmith in Australia, I used coal, because Gordon was doing blacksmithing and did not need the coke. Coke is used for forge welding, so I needed to make coke from the coal that Gordon had.
Coke is made from coal in a forge by heating the coal to a level where the impurities are removed, but the burning is stopped before it consumes all the coal, what is left is coke, & that can be used for forge welding. I made several blades with pamor & with steel cores, before I ever learnt anything about keris production in Jawa.
In Jawa I used charcoal for forge work. For ordinary forge work you can use charcoal produced from just about any timber, but the very best timber for charcoal used for welding is charcoal made from teak. In the 1980's through to 2000, this was very difficult to obtain in Central Jawa, & most smiths who needed to weld procured teak charcoal illegally, it was very expensive & very difficult to get.
The iron & steel used in making a keris came from various sources. In olden times iron came to Jawa mostly from China & through trade sources, nickel bearing iron came to Jawa from Luwu in Sulawesi. Over the last couple of hundred years most iron and steel has been recycled, a lot would have come from Europe. The steel used would be produced from the iron by forge processes.
A lot of both old time imported iron & more recent recycled iron needs to cleaned of impurities before it can be used for something as demanding as a blade. The cleaning is forge work, & it involves the repeated welding of the material until no impurities are in evidence. In my experience this forge method of purifying iron takes somewhere between 7 & 11 welds --- ie, forge out, bend, fold, weld --- before the impurities have been removed. We can gauge this by watching the little stars that rise above the forge when the material reaches weld heat, and by the reaction of the material when it is on the anvil & receiving strikes.
I've been talking about coke & charcoal & coal, but i reckon most smiths now use a modern gas forge. I still do a little bit of forge work, I no longer have a forge I can do serious work on, I use a transportable farrier's forge & BBQ charcoal, this OK for light work.
A smith can work alone, as I have usually done, but it is much easier if he has one or two strikers. The smith directs the blow with a light hammer, say 2 pound or less, the striker then hits the same place on the material with a heavy hammer, usually something between 8 pound & 12 pound.
The striker whom Pak Pauzan used was a very small man who had a low level of strength, but he had been breaking big rocks into little rocks since he was a child, this was the work of his family who had supplied gravel for road work for many generations. Pauzan's striker was not really strong enough to use a heavy hammer in the normal way, rather he used an extremely heavy hammer --- something above 20 kilos --- & he acted as a fulcrum point for a pendulum, he would swing it down between his legs & he would normally do the down swing twice, then on third down swing he would hit the material on the anvil. It was incredible to watch.
Some smiths in the western world use a mechanical hammer, something like an Oliver:-
https://www.youtube.com/watch?v=KIBeGbhXPBw
this youtube representation is pretty primitive, but if you search "blacksmith oliver hammer" you will get a lot of hits that show more modern refined versions of an oliver, these days I think most smiths who are doing serious pattern welding use enormous electric hammers --- or water driven or steam driven.
There really is no traditional apprenticeship system in this area of work in Central Jawa, a man can work as a striker until he thinks he knows enough to set up shop for himself. There are whole villages that are smithing villages. Not many smiths can forge weld.
The old way of making any smith's product & using strikers was for the smith to have a number of strikers --- called"panjak" --- maybe 6 or so men, and rotate them so that no one man could ever get to understand the full process, that full process was normally only taught to the smith's son, or to a man whom he chose to be the inheritor of his knowledge.
The men who make the dress for a keris are specialised workers, they are not regarded as high craftsmen who can be an empu or a pande, but are regarded as ordinary craftsmen or tradesmen. The scabbard & hilt are made by a m'ranggi, or separated, by a tukang wrongko & a tukang jejeran, "wrongko" = scabbard, "jejeran" = keris hilt.
Mendak and selut are made by a specialised jeweller, kinatah work by a different kind of specialised jeweller. The pendok is made by again a specialised craftsman, the engraving & chasing is usually done by a different specialist.
Blade staining is once again a special & separate skill.
In Jawa the names of the specific trade are not used, rather the work is identified with the man who can do it, so we have:-
Pande keris --- keris smith
Warangan --- blade staining
Warongko --- scabbard maker ( m'ranggi wrongko)
Jejeran --- hilt maker ( m'ranggi jejeran)
Pendok --- pendok maker (kemasan)
Mendak/selut --- mendak/selut maker (kemasan)
the pendok maker usually employs the engraver or chaser.
Your question about "spiritual powers" is not one that I am prepared to answer, you need a very considerable foundation before you could be expected to grasp even the beginning of the most basic elements of this. I apologise for my bluntness.
However, I can say this:- the making of a keris as a pusaka, or family heirloom, involves very much more than the simple processes i have tried to explain above, it involves the selection of the material to be used, the selection of days to be worked, multiple offerings, the use of specific mantras during the work, and other attached ceremonies. To the best of my knowledge only one Empu during period following WWII has had this knowledge, he is now retired & his son has taken his place.
The father is Jero Mangku Pande Ketut Mudra, he lives in Bali, he would only make a keris such as I have written about, for a pura (temple) he would never accept an order for such a keris from a person. I first met Ketut Mudra in about 1980, he was working with his father, the family had been the pandes attached to the Klungkung Puri (palace) for many generations. I last spoke with him in, I think, 2024. He is currently not in good health.