When it comes to combining search results, it’s useful to familiarize yourself with Lightroom’s collections features. A selection offers only a temporary way of linking images together in a group, and as soon as you deselect a selection or select a different folder in the library, the selection vanishes. Of course, you can still choose Edit > Undo, or use the keyboard shortcut Command-Z (Mac) or Ctrl-Z (PC) to recover a selection, but the main point is that selections offer only a temporary means of grouping images.
If you want to make a more lasting picture selection, you can convert a selection to a quick collection by choosing Photo > Add to Quick Collection or by pressing the B key. Any images that have been added to a quick collection will be marked with a filled circle in the upper-right corner in both the Library Grid and Filmstrip views.
A quick collection is remembered even after you quit Lightroom—no saving or naming necessary—and the images remain grouped until you decide to remove them from the quick collection. The quick collection can be accessed by clicking the Quick Collection item in the Library panel (see Figure 1). You can also choose File > Show Quick Collection or press Command-B (Mac) or Ctrl-B (PC) to display the quick collection images only and choose File > Return to Previous Content (press Command-B or Ctrl-B again) to restore the previously selected image selection in the content area (see Figure 2).
Figure 1 To view a quick collection, click the Quick Collection item in the Photo Library panel.
Figure 2 Press Command-Alt-B (Mac) or Ctrl-Alt-B (PC) to save a quick collection as a permanent collection to add to the Collections panel.
Quick collections let you view images from separate folders, group them as a selection, and save that selection while decisions are being made (see Figure 3). Quick collections remain "sticky" for however long you find it useful to save them as such. However, after you’ve saved a quick collection as a permanent collection, it’s usually good housekeeping practice to clear the quick collection, which you can do by selecting File > Clear Quick Collection or pressing Command-Shift-B (Mac) or Ctrl-Shift-B (PC).
Figure 3 One of the advantages of creating quick collections is that you can create one from images contained in separate folders and then select the quick collection to view an accumulation of all the selected images. In the example shown here, I marked images from the Antarctic, Oslo, Stockholm, and Chicago folders as photos to add to a quick collection. When I clicked the Quick Collection item in the Library panel, I was able to view the images from these separate folders simultaneously.