For the last few years, everything we've been accustomed to re gold size, has changed. I suspect this has to do with EPA regulations in the USA.
Over the pat couple of years, I've had all sorts of problems with size not reaching tack when it's supposed to. If you gild, & have been having similar issues, I may have a solution.

Urban J Billmeier ( W&B Gold Leaf) ran into a guy ( the name escapes me but he's considered one of the elite among gilders) in Chicago, & brought this issue up. He said......
" In the last year or two, the hardener in size has been changed, & where we once needed to to shake or stir just a wee bit ( LeFrancs was "stir" only), apparently, we now need to STIR for about 2 or 3 minutes, to get this hardener evenly distributed within the can. Since I've started doing this, I've had no further issues ( other than taking too long for lunch & losing my tack, which is no-one's fault but my own).

I mostly use DUX size, but I keep Lefrancs on hand as well. I've taken it from the original container & put it in a 1/2 pint can. Now it can be stirred with ease.

Also, we used to be able to mix 3hr & 12hr sizes together, to get a convenient time for the size to reach tack. Apparently, with the new formulations, we can no longer do that, at least with Lefrancs.

I'm definitely no master gilder nor chemist, & I'm just repeating what I've been told & have reason to believe is accurate.