I quite often turn willow for larger pieces , but haven`t done a pen for years . The colour absorption pattern intrigues me . If I`m reading the photo correctly , you used a straight grain piece of wood , yet the dye pattern is diagonal . Did you mechanically abrade the wood to achieve that , or is it just natural variation within it ? I have never dyed willow .
Willow can have very attractive spalt colour variation as well . Some have sapwood/heartwood boundaries that are sharp in colour change , hardness , and rot resistance , all in the same piece . Translated , that means soft , white , easily rotted sapwood , and fairly hard , red . very rot resistant heartwood .
A figure I sometimes see is the presence of birds-eye structures , but smaller than you might find in birds-eye maple . They might take the dye in an interesting way . Unfortunately , I can`t give you any guidance on what to look for on the tree to find them . If you know , please tell me .
The last feature we commonly see is what we call diamond willow . It is apparently caused by a fungal infection of of a developing branch , which kills the branch , causing the tree to develop a diamond pattern in the heartwood around it , leaving that portion of the heartwood essentially unprotected by bark . It is most common in Bebb`s willow , which is an upright growing , upland species - that is , it doesn`t tolerate wet feet . It was commonly used by the pioneers here (some Norwegian) for fence posts . However , pussy willow also occasionally develops diamonds in our conditions . It is a larger tree , likes damp feet but won`t tolerate flooding for more than 2-3 weeks , doesn`t mind growing a trunk at 30-45 degrees from vertical , nice spalt patterns , not very rot resistant heartwood .
Please don`t ask me to describe the salient features of the other 40 willow species native to Alberta . I can`t !