Instructions
Learn to identify it. Ironstone is usually creamy white, but painted designs or transferred patterns on white are common. Blue ironstone is less common. Ironstone is always opaque and has a heft that neither porcelain nor earthenware has.
Train your eye to recognize it by looking at a lot of it. Visit antique stores and talk to the owners, who will probably be happy to show you the registry marks and tell you about them.
Turn a piece of ironstone over and you will often find a registry mark. In a PDF offered by White Ironstone China Association, you can see images of the original Charles Mason mark, which is a diamond with a large R and small d in the middle. The d is underlined. Sometimes no mark means that the piece is so old that its manufacture preceded registry marks, so don't toss an unmarked piece without finding out more about it.
Consider collecting only pitchers, zeroing in on pieces from the 19th century, or narrowing your focus in some other way. Collecting anything becomes expensive without a focus---not to mention that you may also find your house starting to look like a rummage sale.
Go out and find it! Ironstone can still be found at yard sales, so be ready to begin a new hunt every Saturday morning. Auctions, too, often yield a pitcher or bowl or cup and saucer. Once in a while you may find multiple pieces of sets. You can save time by attending the auction preview. That way, if there isn't any ironstone, you won't be sitting through the entire auction wondering if any will pop up. You can also leave an absentee bid at that time if you don't want to attend the auction.
Like yard sales, estate sales may turn up ironstone that has been around the house so long that the family doesn't value it anymore. And nowadays, eBay is a good source. And of course, antique and collectible shops often have it in their inventory.
Be wary. If you're looking for pieces that are old enough to deserve the antique label or at least be designated a collectible, there are many new pieces floating around and some dealers will let you believe they are old.
Also, chips, cracks, repairs, crazing, lost components (such as a soup tureen lid) and discoloration all may lower the value. If you are a serious collector, you may not want to bother with those pieces. If you're a casual collector, a tureen with a repair will probably look just as pretty on your sideboard as one that's perfect, and you'll be able to purchase it for very little money.
Expect to pay, but how much? Prices of ironstone run from a few to hundreds of dollars. If there are any imperfections, pay less than you would for perfection. Also, you can expect to pay less at estate and yard sales than you would at an antique shop.
Knowledge is power. Buy a good book on the subject and peruse it. You'll learn a great deal about registry marks, decorative patterns, shapes and prices. Then stash it in your car so you can easily consult it when faced with a buying decision.