Robin Lee and write out a couple's wedding vows. They had been intrigued by the Ketubah tradition and wanted something similar that could be signed during the ceremony. Since they liked Robin's work, they commissioned a painting from her that was then sent to me to write on. I've written on canvas with metal pens before but not on surfaces done by others, so I had to do a little research to make sure it would work. I ended up spraying lightly with a fixative to give the acrylic paint surface a bit of "grab" and then used acrylic gouache so I could have more control over flow. It was still a little erratic but did OK. I worked out a style that seemed to fit the painting style and could be done at a size to fit the wording (it is a the shorter of two versions sent me, fitting in more just wasn't going to work)
You see the signatures added on Robin's facebook page
And here's a closer look at the lettering, done with a clipped EF66 nib and acrylic gouache with a little acrylic black ink added to get it dark enough since I usually only have red, yellow and blue in acrylic gouache. Of course, to ensure the fairly "flush right" margin I had to do some extra layout and tracing work.
Here's an example of a Ketubah by a calligrapher I know, and a gallery-full by another . I have done a wedding certificate or two where all the guests sign it, such as for Quaker weddings.