If your workflow involves stacking before keywording then you have probably found that the keywording part is either inefficient or incomplete. Adding keywords to a closed stack only adds to the pick, so those non-picks remain without metadata.

There are consequences to this. For example, if I change the pick after keywording, the new pick (and hence the stack) no longer has the keywords:

The water keyword will not find the pick and so will not find the stack. And unless I specifically select to ignore stacks, any smart album that filters on the water keyword will fail to find this image.

The choice I have is either to live with this behavior, or keyword every image in the stack when I do the keywording. But how to keyword every image in a stack without going crazy?

The obvious way is to select the pick, click the number to open the stack, then click drag, click drag each keyword to each image:

This is very slow and error-prone. A faster way, but still with too many keypresses, is to open the stack and select all the images in the stack at once with command E. Then each keyword can be dragged over from the HUD just once to apply it to all the images:

I can apply multiple keywords at the same time by command-clicking on them and then dragging, saving even more time. And if the keyword buttons are set up on the keyword bar at the bottom of the window, I can press them or their keyboard equivalents to quickly apply commonly-used metadata.

I actually use an even faster way that goes straight to the next stack and opens it all in one step. First I select the top image in the project or album, then press option page down. That single key-press seeks forward to the next stack, opens it, and selects all the images it contains. Now I simply add keywords to all the images in the stack, as before. I press option page down again to go to the next stack and repeat. Once done, I close all the stacks with option semicolon.

Option page down also works in list view, but in list view the images are to small to be recognizable.

The option page-down method for dealing with stacks skips all the intervening unstacked images and that can be inconvenient. I have to go back over my images picking out the ones that are not in stacks among those that are in order to keyword them. I can make this a little easier by sorting the display by Keywords:

Once I do that, all the non-keyworded images are together at the bottom of the browser ready for keywording.