Dear Michelle,
Your printer ink is acid free, the only problem that might occur is that the ink is NOT water or fade proof. This is not a real biggie as far as I am concerned, unless you plan on letting your book get, wet or sit in the sun all day. As for as the postcards, they can be tested with an acid testing pen, or sprayed with a product called acrhival mist, kinda pricey at about $40.00 a bottle, but it can be purchased at Micheals craft stores with their 50% off coupon for $20. during their sales, and one bottle lasts a long time, and I feel it is a must for a scrapbooker who has a lot of assorted treasures to add and want to be safe. The best way to add materials that you are not sure of is to put them on a separate page of a double page spread, with perhaps some journaling or die cuts, just not on or touching any photos. Penny