Originally Posted by feline fanatic

In most cases it is easier to mark before but there are many variables.

If you are tracing your design using a light table you will absolutely have to mark prior to sandwiching.

How are you quilting it by machine or by hand? I am assuming because you ask about sandwiching you are not loading the quilt onto any sort of rack setup. Will your sandwich be pin basted, hand basted or basted via adhesive method or with a fusible batting. If using a fusible that will require heat and some people also use heat when using elmers school glue to help set the adhesive quicker, you will need to wait until AFTER you sandwich to mark as so many marking tools become permanent after you apply heat or in the case of frixon pens go away. But if you are pin basting or thread basting you can use a frixion pen or blue water soluble marker or washable pen. As long as you don't iron the quilt after marking or apply any sort of heat (even sitting in a car on a hot summer day will be enough to set many marks.)

Lots of handling will make chalk markings rub off long before you are ready to quilt so if you are using chalk of any kind (chalk pencil, pounce pad, chalk roller or school chalk sharpened to a point) or the white ceramic pencil I can tell you from personal experience just the basting process will remove the marks. So if you are using a stencil and chalk I would recommend marking as you go after sandwiching.

Air soluble pens disappear to quickly so those you also have to mark as you go.

So it all depends on how you are sandwiching and what tools you are using to mark and how you plan to transfer your design.