I have a 13mm gallstone or stones and found this natural cure on line, is it valid and effective for my size stone or stones?

This method to remove gallstones naturally is probably a traditional European remedy. I learnt it from a Taiwanese, Dr Lai Chiu Nan, a chemistry dortorate holder and former cancer researcher in one of America's top cancer research institutions, who now teaches natural health.
Dr Lai Chiu Nan visited Singapore during the early 1990s and gave a number of free lectures, in both Chinese and English, attended by capacity crowds at the Singapore Indoor Statium, which seats about 12,000 people.

After attending her lectures, I wrote an article in The Good Life, on how to remove gallstones naturally. I have since seen excerpts of that article reproduced in all sorts of places, including pamphlets at health stores, websites and blogs.

Possible 'dangers"

Before I pass on this method to remove gallstones, I should point out that some doctors have warned of its "dangers". They say that, if the gallstones are too big, they might end up being stuck in the gall bladder ducts and this could be dangerous.

In theory, this might happen. So if you are afraid, don't do it.

When you embark on natural remedies, whether to remove gallstones or for other purposes, you need to take responsibility for your own health and I shall not be held liable for any harm or danger that you might experience.

At the same time, when you embark on natural cures, it helps also to understand the reasons behind some of the procedures.

In this case, part of the method to remove gallstones naturally involves drinking plenty of apple juice for about a week. It is believed that some substance in the apple juice, probably pectin, helps softens the gallstones to that the risks of them being stuck in the gall bladder ducts are minimised.

In any case, if you lack the confidence, don't do it.

Just be aware also that surgery and other medical procedures to remove gallstones UN-naturally also come with their own set of risks.

You decide which risks you wish to take.

Possible instant diarrhea

Another possible side effect of this natural way to remove gallstones is "instant diarrhea" at the last step, on Day 6. See below.

I write this from personal experience. Luckily, I was at home and the toilet was nearby. But I have not heard of anyone else with a similar experience. But just in case... do this gallstone removal remedy at home, and do the last step nearby a toilet.