Tack heads needed to be smashed to achieve the desired head diameter since head diameter determines brightness. There is also a wide variation in tack head sizes, especially with the aluminum tacks, so sorting and selecting was required. I didn't figure all of this out ahead of time, so I had to go back and redo many copper and aluminum tacks. Turns out I did too much head smashing in certain areas, so I had to redo my redo. To keep the copper tacks from being too dark, I had to switch most of them to a larger size. I almost gave up on the entire project several times during this period of repeated challenges. I managed to only smash my fingers once.