Hi everyone,
I’ve been asked by a friend of mine if it were possible to create a more or less intricate patterned patina on a brass whistle on purpose.
I suppose it is possible, however I have no idea how to do it. Maybe leaving out the whistle during a full moon night after bathing it in unicorn’s blood would do the trick? 
If the whistle is lacquered, you’ll have to take that off. Nail polish remover should do the trick. I don’t know about moonlight, but leaving it outdoors might work. You could even bury it in the ground for a couple of days (cover the windway and other delicate areas with plastic wrap?). There might be chemical ways to do it, but I don’t know how.
There was this recent suggestion: https://forums.chiffandfipple.com/t/patina-on-burke-brass-whistles/63303/2
If you’re into applied chemistry, this page has recipes:
http://www.architecturalclassics.com/blog/how-to-age-brass/
Thanks squidgirl and MT. I’d already found the old entry on the board before I posted this new topic, but thank you anyway. 
I’m going to read my way through squidgirl’s link now. Maybe, if I have the time and the brains to understand what they’re writing there, I will post a summary in this place.
translated to German 
Altern von Messing
Short extract:
Salz und Essig
Salz und Essig sind großartig … Leider müssen Sie diese einzeln kaufen, also keine Entschuldigung für den Kauf von Chips! Sie können mit einem kleinen Pinsel Essig über die gesamte Oberfläche des Objekts auftragen. Dieses oxidiert das Messing, das ist eigentlich, was passiert mit dem Metall - natürlich im Laufe der Zeit, der Prozess der Oxidation. Bemalen mit Salzwasser hat die gleiche Wirkung, nur braucht es ein bisschen mehr Zeit und Geduld.
Some other links treating the same topic:
http://www.sciencecompany.com/patinas/patinaformulas.htm
http://www.uniquelighting.com/Spec%20Sheets/PatinaTreatment.pdf
http://www.fxl.com/learning/patina.htm
What I have found out so far:
Storing one’s whistle in a place with high air humidity will accelerate the patination process.
Exposure to oxidative acids (= acids containing oxygen molecules), such as vinegar, lemon
juice or ammonia leads to patination. The lower the acid’s pH-value, the faster the
patination process.
Exposure to saltwater will over time create a patina.
And then there are still the exposure to heat/flame and a whole lot of ready made chemicals as well as a great many mixtures made of chemicals bought at the drugstore. Needless to say they’re all far more dangerous to one’s health as the others mentioned above.
hans: you’ve actually managed to find a more or less accurate translation program. - A small miracle in the world of bad machine made translations. 
You could do patterns by applying bee’s wax to areas you want to keep patina free or kept ‘unharmed’ then apply vinegar to the whistle. I’ve used this method to etch the blades of knives I’ve made. Etching takes longer with such a mild acid as vinegar, but to get a patina happening doesn’t take too long at all.
Experiment on a small plate of the same sort of metal as your whistle, in this case it would be brass if I remember correctly.
Mick
The link was to a machine-translated page using Google’s language services.
In the past I used Altavista babelfish, but found that Google seems to do a better job. Of course this may well vary from language to language.
The quoted translation was from Google, but I sorted some errors manually.
Cheers,
Hans
A little heat with propane torch and spraying with water will do so. But don’t get it too hot or you’ll melt the plastic part. Also, too much heat and sudden cooling will soften the brass.
Thanks for the hint, Daniel. While melting the plastic fipple wouldn’t be a problem, mine is a tunable Dixon Trad, so I can take off its head completely.
Using a torch is something else. While I like open flames on candles or in a bonfire, I’m not likely to buy a torch or bunsen burner and take it home. There’s too much wood in this place.