if you plan to put the quilt together before writing you want to use pre-washed 100% cotton fabrics- washed with detergent-no fabric softener. use a tear away stabilizer on the back of each square- this will give some stability and help keep the ink from soaking through onto what ever is behind it. use micron pigma pens- they are permanent, acid free, archival quality- do not bleed or fade. at my daughter's wedding reception we had 100 prepared blocks (10" squares cut, ironed onto freezer, framed with painters tape- in a stack on a table with an assortment of colors of pigma pens- the guests enjoyed grabbing a block and sitting down to write words of encouragement, advice, draw pictures, personalize their messages- after the *festivities* were over I took the blocks home & constructed the quilt- turned out wonderfully...if the quilt is all together ahead of time the amount of time the guest will spend will be very limited- you may want to reconsider- it's not that easy for some people to write/draw when something is hanging- where if they can sit down with a block they tend to (enjoy) the process much more & it shows.