Well whether or not to etch a kris is a personal thing. On one hand it may devalue the blade as many western collectors do not like any alteration to be done to any part of the blade. However a moro (Im using this term loosely as since I do understand the perjurative connotations associated with it)would never let their blade fall into such disreapair and would keep their in a good working condition with a keen edge and a good etch. I personally etch because I would not dare disrespect the blades by not caring for them and also I know that I will never sell anything in my collection. I am not concerned with monetary value as much as I am with keeping with cultural tradition. So I guess in essence its really up to you. Are collecting blades in order to have some kind of monetary investment, or are you a caretaker of the blade who wishes to keep with tradition and respect the spirit contained within?
As for whether ferric chloride is a good etchant I would have to say its what I use now for my moro swords. Traditionally in the Philippines the etch is done using various citrus fruits but I have been quite happy with ferric chloride in its ease of use.
I normally start out cleaning the blade by removing all rust using diluted lemon juice. Then if the blade is in poor shape with many pits I will try lessening them with the various grades of sandpaper. However I will not try to remove all the pits or chips. A few add character, but too many just hide the damascene patterns. After sanding or in cases in which sanding is not needed I polish using a metal polish. Next I degrease the blade using rubbing alcohol, another route is to use an ash and water mixture which would be more traditional and works well but its taken me a while to save enough ash to be used properly. Now traditionally a moro would leave their blade out in the hot sun, but since I live Minnesota hot sunny days are a rarity so I use a blow dryer to warm the blade. Finally when the blade is warm I stand it up and brush on the etchant. I prefer standing the blade up versus immersing it in a tray of etchant since it saves on etchant. The thing is just to keep the blade properly moist with etchant. Its not quite as hard to do as it may seem at first and after about 15 minutes depending on the coloration Im finished. Now the proper coloring of moro blades is something that one must develop an eye for. The two kris I have pictured were etched a while back so are in need of a re-etching. I normally like them slightly darker. It is said that moro's prefered the etched blade over the buffed shiny blade so that they would not shine and thereby reveal them in the jungle.
As for a substitute for the lime arsenic solution used in Malay keris there realistically is no proper substitute that will give the proper color contrasts. There are people out there that will patinate keris for you, and there is always the option of going to Indonesia and attending a keris etching ceremony (though this is quite a spendy trip just to clean up an old blade
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). Cleaning very rusty/dirty keris with diluted lemon juice can really help its appearance, but again to get the proper blacks there really is no substitute for the traditional method.
If you could post any pictures of your kris it would make it much easier to determine the best route to take. Again I must say to ask around the ethnographic edge forum. There are many much more qualified and learned keris collectors there. Also here are a few names of people that may be able to help you: Cecil Quirino of Kris Cutlery is probably the most knowledgeable person in the US on keris and kris, Philip Tom of Seven Stars Trading company is a generally good person and experienced antique restorer, and Erik Farrow of Eriksedge.com is an outstanding gentleman who is very knowledgeable and generally nice guy these two kris that I have posted were purchased from him.
Well Im sorry I couldnt be of more help, but I still consider myself a novice in the realm of keris/kris collecting. Please come over to the ethnographic edge forum as there are many more qualified people than I, or ask any of the people I have listed for help. They may have other options that I cannot think of.