Among the resource types then used were ICN#, ICON, and others. This shows some of the resources of a Classic version of QuarkXPress. Customising icons in QuarkXPress using ResEdit. Instead of an app consisting of nested folders containing resources such as executable code and icons, these were all stored in resources. Icons in Classic Mac OSĪpp bundles were introduced with OS X to replace the previous single-file structure of apps in Classic Mac OS. What’s going on is more complex, and takes us back to a bit of Mac OS archaeology.

If you try copying that Icon? file to another folder, you’ll discover that doesn’t change that folder’s icon at all, though. Instead, whether you’re adding the icon to an app (or other bundle) or a regular folder, it’s saved in a hidden file named Icon? just inside the folder. When you add a custom icon, that isn’t changed at all. Normally, app icons are set by the developer, using the AppIcon.icns file in the app, in the bundle path Contents/Resources.

You can also do this with individual documents, and with volumes, although custom volume icons can cause problems when they’re shared in Ventura, it appears. You can’t do this any longer with bundled apps, though, as Ventura breaks their signature if you try making a copy of them to a folder on a writeable volume. A couple of seconds later, the custom icon should appear correctly in the Finder window. Select that icon, and paste it into the original in the top left of the Get Info window. In some cases, you may need to open that PNG file using Preview to make this work, but you should be able to do this direct in the graphics editor once it’s in PNG format. Make the changes that you want to it, and save it as a PNG file with Alpha (transparency). Select the image at the top left of that dialog, copy it, and open the pasted image using your graphics editor. Select the folder or icon you wish to customise, then Get Info on it. Here I’m using the new version 12 of GraphicConverter. To create a custom icon you’ll need a decent graphics editor capable of working with PNG files. This article explains how to do that, how it works, and goes on a brief archaeological dig into the history of Mac OS. Giving special folders their own icon makes them more distinctive than simply applying a tag to them. You might have more than one copy of an app, or two different versions which by default use identical icons. It’s sometimes valuable to be able to customise icons for folders and apps.

Big sur custom folder icons