extension tubes - a 12mm will give you a moderate increase on your minimum focus distance, a 25mm will get you pretty close and anything more and your front element will nearly be touching the subject. Whether or not you'll get 1:1 magnification is another matter that will require research.
I use a 12mm extension tube on my 85 f/1.8 to just allow me to get a bit closer, the minimum focus distance is pants and on full frame it can be rather hard filling the frame with anything smaller than an A4 sheet of paper. Be aware that with extension tubes your focus "area" becomes very limited - with my 85 I think I have only a few inches to play with, so while tubes are great for occasional use they shouldn't replace a proper macro lens. If I did more Macro I'd buy a dedicated macro lens instead.
Extension tubes don't contain any glass, they just move the lens further away from the camera body - so don't go paying for expensive Nikon air when Kenko air (for instance) is just as good
Also be aware that at very close focus distance like CJS shot above depth of field is absolutely tiny - I am guessing CJS shot was done at or close to f/22 - certainly no less than f/11. Macro at f/1.4 just won't work..