The images in the gallery are stored in three resolutions (and file sizes). The coarsest pictures are 2-12K, the medium resolution pictures are 15K-40K, and the high resolution images are 150K-650K, taking correspondingly longer to load. Clicking on a thumbnail will take you to a single image in the next higher resolution.
The image height of the gallery thumbnails is set in "ems", so that resizing the text (in the browser's preferences) will also resize the pictures in proportion. If you would like to change this proportion, for example to enlarge the thumbnails without enlarging the text, simply select the height you would like in the dropdown menu in the upper right of the gallery (but illustrated on the left of this paragraph), and click one of the buttons next to it (fast or fine, depending on the image quality you want). The images will reflow onto the page in the new proportion.
By default (fast), the thumbnails are the coarsest of the three resolutions, and clicking on one will take you to a medium resolution version. This is done so that the pages load quickly, but if you are on a fast connection you may want to see nicer pictures. Going to the next level (fine) in the gallery will load the medium resolution photos as thumbnails, so that clicking on them will take you to the highest resolution picture.
Since the thumbnail already shows what the pot looks like, to save space on the page the caption only includes the size of the piece. However, if you hover the mouse over the image, most browsers will show a longer description of the pot in the hovertext. What looks like a catalog number is actually the picture number, and though not unique, is helpful in identifying a particular piece.
A web page is a set of suggestions to the browser; it is the browser's responsibility to execute these suggestions to the best of its abilities, taking into account the limitations of the user's hardware, software, and preferences. Few web designs are perfect, and not all browsers implement web standards equally well. If you encounter problems with this site, Email the webmaster, describing the bug and the system (Max OSX, Ubuntu Linux, Windows XP, etc) and browser (Firefox 44.0.2, SeaMonkey 2.38, Opera 4.0, Internet Exploder 5.5, etc.) you are using, and he will flog somebody until the site behaves properly.