I started with one of the straw sun hats I bought from a thrift store (they had several for about $0.50 a piece, and these can be awfully useful as hat blanks). Most of the hats I bought at that time were undecorated, but one had ribbons and fake flowers stuck to it with large amounts of hot glue. The flowers and ribbons came off, but the glue would not, so I took several rows off the brim (where there was no hot glue) to add to one of the undamaged ones to make this colonial hat, but I never threw away the one with the glue, which you can see in the background of this picture.
The first thing I needed to do, though, was change the shape some. The crown of a modern sun hat is way too deep for an 1870s lady's hat, so I soaked the straw and started trying to flatten it. I could only change the shape so much doing that, so I ended up with this.
At that point, the project got set aside for a little while because I certainly couldn't fix it quickly enough to wear it that night. Later, I decided to flatten the crown without taking all of the decorations off (though I did remove the bulkier, pinned-on portions), so I used a utility knife to cut the stitches between the rows of straw just on the funny-shaped part of the crown of the hat. I cut off some of the very center and re-wet the straw as much as I could without soaking the fabric and lace, making the straw more maleable.