That's right folks, we've added hot foil stamping to our repertoire of specialty in-house processes. One of the best things about foil is, unlike our letterpress inks which are transparent, foil is opaque, allowing us to apply a lighter color on a dark background (see this blog post to read about letterpress printing with white inks on black stocks).
As designers we love(!) tiny type, but as printers, we know there are limits to what is realistically achievable. With that in mind we created a set of specimen cards, exploring different type sizes using the two fonts we use for our identity. From the reasonable 11pt type all the way down to the petite 5pt italic Baskerville, the foil held up pretty well, though the fidelity at these sizes can't always be guaranteed–it's going to change from typeface to typeface.
With letterpress printing we recommend tracking out your type (at least to 25 or 50) to give room for impression between letters. For foiling we recommend the same, this keeps letterforms from merging into one blobby mess on press.
We found that the metallic foils (gold, silver, copper, etc) released a lot cleaner than some of the pigment foils (colored foils, such as the blue foil shown below). We definitely wouldn't recommend getting too tiny with the pigment foils.