Last August I wrote a post titled Breathing 101. That post gave the reader the Lamperti School method of breathing, while this one features the teaching of the García School which I have quoted below from Pauline Viardot-García's An Hour of Study (1880). If you compare them, you will see the similarity at once, which consists of breathing through the nose for a very long time. The difference? The Lamperti School put a number on the practice, which entailed inhaling and exhaling for 18 seconds.
4. The pupil must breath very slowly and very deeply, through the nose, with the mouth closed; and the breath must be held a moment before commencing each exercise. Too much pains cannot be bestowed to the habit of taking a long inspiration through the nose. -Pauline Viardot-García, An Hour of Study, (1880)
How to apply this practice while singing repertoire? That's the trick really, if you can call it one, which it isn't at all. It's actually quite simple, the point being to maintain the feeling of breathing through the nose even when the mouth is open. How is that possible you ask? Doesn't the singer want the soft palate to be up and sealing off the nasal passages when the mouth is open? Yes, that's undoubtedly true, but it won't prevent the singer from feeling as though he/she is still breathing through the nose. If you breath long enough in the proscribed manner, you will feel the muscles of your body, including those of your head neck and face stand up, that is—extend. If you've been reading my recent posts about the ear and the voice, you will have some idea of what this means. There are many things that happen when we breath, and if we know what we are doing, one of those things is to help the ear do its job, which is to awaken when we sing.
My take from all of this? The Old School was a lot smarter than some of us believe it to have been with its supposed reliance on imagery. On the contrary, they seemed to have made a science of essential practice.