What are some good substitutes for ferric acid to etch demascus. Any home concoctions?

Simple vinegar

Hot vinegar super saturated with salt.

Lime Juice

Coffee

Tea

Soaked in a bog high in tannic acid

HCl

HNO3

H2S04

Note that the strong acids are much more dangerous to work with!

The food based one will not provide much in the way in topography but often provide interesting colour effects.

Equal amounts of table salt and RootKill (copper sulfate pentahydrate) in water. 1/3 to 1/2 a cup of each in a quart of water.

Anybody actually use the tannic acid? I've got two quarts of distilled oak tannins, I might try it.

I have using strong loose leaf black tea "sludge".  Purple black colours, no topography,  First time I left it in the etch overnight and the next morning it looked like my piece had grown fur. I thought well that didn't work and went to wash it off and the glop slid off leaving the purple black colours.  (I was trying the suggested echants available listed in "The Sword In Anglo Saxon England" H.R.Ellis Davidson

I don't have any home brew to add to the  food based ones already mentioned but I have made some pretty stuff using Brownells cold gun blue. If you've never used it its a one part product, no mixing. It colors fast and cleans up with water. You wont have any silver color when you're done, even the high nickel stuff will be a cool, light blue and the high carbon will be almost black but the whole piece has a "wet" look when it's dry. Most gun shops/pawn shops in my area have the kit for under $10.00.

Have you ever then burnished the high layers? (etch for topo and then blue and then burnish to bring back the bright layers?)

I put a blade on the buffer without any compound once after bluing and it brought the highs to a lighter blue but not back to silver. I didn't try to go any further with it because I really like the light, "smokey" blue look. I am open to experimentation though!

I was using a hard arkansas black and WD40 on a flat grind.