Mr. Maisey i agree with your traditional way to stain a blade....but with some old blades sometimes for me it is really very very difficult to have a good result.
About temperature... some years ago during winter (where i live the temperature is not far from zero) i tried to stain an old bugis keris. I remenber it was very cold and i used warangan (mixed some days before together lemon juice )by a tooth brush on the blade. Well... it was so cold that i used always my fingers to dry the solution (with the help of a electric phone).
When i finished to stain the result was, with my great surprise, very good
