Since I'm notorious for leaving coffee stains everywhere, i felt challenged when i read on a knife-makers forum that coffee gives good contrast on damascus.
So, i selected a Bali tourist/soldier keris, i couldn't successfully stain with FeCl3, and made a lot of coffee....
First i followed the instruction given on the other forum and prepared the coffee with two spoons of instant-coffee per 200mL of hot water. Meanwhile the keris is degreased and etched for 2-5min in citric acid. The keris is then fully submerged in the still hot coffee. The pamor became visible after 2h and reached its maximum contrast after 6h. The result was rather disappointing. After drying the pamor was barely visible.
Next i repeated the procedure with "real" and strong coffee. That lead to the same result after 2-3h.
For the final experiment i added a teaspoon of citric acid to the coffee (about 4L). This gave a remarkably good result after about an hour (see photo). Leaving the keris longer in the coffee proved counterproductive as the contrast began to degrade after the coffee cooled down.
After the promising results i tried to stain the keris from this thread
http://www.vikingsword.com/vb/showthread.php?t=13829
with the same mixture. However, this time the result was very poor.
Conclusion: Coffee may for some keris be a viable alternative to FeCl3 but may fail miserably on others.
For good results the coffee has to be hot and slightly acidic.
Best Regards,
Thilo