After listened to Steve I quickly pulled out my harps in C and D I used to play mainly Blues but now I’d like to try ITM, and I question myself, how can I do those little “twiddy bits” so nice,those ornaments that it can be easily done on a whistle?.
Does someone knows the techinques to make slides, cuts and graces notes on the harmonica, is it possible? 
The long reply that follows is extracted from “one that I did earlier” for a harmonica publication. It is definitely not the last word on the matter. It is aimed at the player of diatonic harmonicas (blues harps and tremolos) rather than chromatics. Moreover, I don’t tongue-block at all, so there may be possibilities for ornamentation that I haven’t mentioned. I should add that I strongly recommend that blues harp players consider retuning their harps to the Paddy Richter tuning (it’s a retune of just one reed) to enable the playing of far more of the tunes than is possible with the standard tuning. Details on my website.
<<QUOTE: The bad news is that harmonicas in general are not ideally set up for ornamentation in I.T.M., but all is by no means lost. Even the traditionally-used instruments have their limitations too, and there are things you can do on harmonica that are out of the reach of some other instruments. I will attempt to give an idea of what is possible on the standard 10-hole diatonic, but most or all of what I say will apply to tremolos and chromatics as well.
- What I would call the “cut.” This is a single, fleeting note of almost no length at all played at the start of the main note, using the same air direction as the main note. You can achieve this by moving the harp rapidly, but I strongly recommend that you instead employ a rapid sideways flick of the lower jaw. With a little practice you will find that this helps to get the desired effect much more reliably. You may feel that the note achieved is not at the correct pitch, but this is not a cause for concern at all if the note is played, as it should be in any case, very fleetingly. Be sure that the cut is not allowed to increase the overall length of the phrase – a serious mistake often heard, alas.
- The triplet. This is when you play three notes within the normal length of two, giving a pleasing lift to the phrase being played. Triplets can be played with change of air direction, for example blow-draw-blow, or all in the same direction, such as all-draw. I often use 6D-7D-6D for instance. A common triplet is 6B-6D-7D at the beginning of a phrase. To get the rhythmic effect that you want to achieve it is vital to give equal length to all three notes. Triplets which replace a single longer note using the same air direction for all three notes can almost sound like a roll - very effective in some reels and hornpipes for example.
- “Tongue-percussion,” often decried by the experts, but I think it has its place. You can use this effect as an alternative to the cut, or it can be there in its own right. It is achieved by tonguing “diddley-dee” with the tongue touching the roof of the mouth behind the upper teeth, all on the same note. It is useful for occasionally breaking up a longer note, especially in reels. Try to think of it as a percussive effect rather than a melodic device. A great Irish fiddler, Tommy Peoples, achieves an analogous effect by bouncing the bow on the string.
- For tongue-blockers…you can use tongue-slaps and octaves/split intervals as in other types of music. Bringing in these harmonica techniques to I.T.M. helps to give the harmonica its own voice or character, without sounding “alien,” as long as they are – along with everything else – used judiciously. Tongue-blocking can also be used to provide a “vamping” accompaniment to the melody.
- Note-bending, used for decoration as opposed to obtaining accidentals. This is a very valuable skill to have. The use of bending, executed with good taste, adds real expression to the music. It is particularly useful to be able to bend the high blow-notes. You need not be obsessed with the tonal accuracy of your bending as you are using the technique as decoration only, but I would certainly advise you to listen critically to recordings of yourself to ensure that you are not overdoing the bending either in quantity or frequency, a temptation that’s easy to fall into – I speak from experience!
These days you can buy specially set-up harps, ones that may have started out life as chromatics, for easier Irish ornamentation. If this sounds interesting to you visit Brendan Power’s site at www.brendan-power.com
To sum up and conclude this section: ornamentation is first cousin to that other skill that I touched upon earlier, variation. These two “tools” are regarded as essential attributes of the experienced player, and the way they are used is very much up to the individual musician. If you see ornament markings in tune-books, always regard them as suggestions only. Aficionados of I.T.M. will be judging, unconsciously, the quality of the music by the way the musicians “add lift” by the use of variation and ornamentation. There is no “correct” way to ornament a particular tune. You will sometimes notice that the musician plays different ornaments, or puts ornaments in different places, upon the repeat of the tune or section of tune. If there are any “rules” applying at all, they state simply that the use of variation and ornamentation should be governed by good taste and respect for the tradition. Writing about these things has quite limited value: only by listening incessantly to good musicians will you get a “feel” for what is right. I hope, however, that I will at least have pointed to what you should be listening for. For a harmonica player starting out in I.T.M., and for everyone else come to think of it, I can only repeat the advice that less is more! UNQUOTE>>
Cheers!
Steve