The 'new Drawable' actions are executed in the Draw method. I just pass them directly as an argument instead of using a variable like you do. I am planning to add an extra syntax soon (https://magick.codeplex.com/workitem/1384) that should be something like this:
And it is better to be using the 'using thing'. Magick.NET uses unmanaged memory and the using makes sure it is cleaned up properly.
image.Draw(new Drawables() .FillColor(MagickColors.Transparent) // -fill none .StrokeColor(MagickColors.Black) // -stroke black .StrokeWidth(1) // -strokewidth 1 );