These are just a few basic suggestions for knife play.
Please note they are NOT intended as a firm guideline and i am not claiming to be an expert.

Using knives as a form of edge play is generally for the intention of causing fear, blood letting, creating pretty marks, insertion and occasionally even permanent scarring.
Knife's are extremely dangerous implement's and for first timer's I strongly recommend that you gather as much information as possible.
It should go without saying that trust is essential on both the Dominant's and submissive's part. Only play if you are in a good state of both physical and mental health.
Knife's are classified weapon's and therefore subject to very strict law's so if you are considering an outdoor scene be aware of any penalty's you could incur, find isolated areas and constantly stay alert for passers by.
For most knife play does not involve drawing blood contrary to popular belief, it is more often than not used as a weapon for such as creating fear. One popular way of playing with knive's is during rape and/or abduction scenes .
They're very often used for abrasion (scratching) and as the blade is metal it can be heated or placed in the fridge/freezer beforehand for bringing the added extra of touch sensation into your play.

Always use a good quality plain knife, (never go for cheap) preferably carbon/stainless steel with a blade of around six inches. Decorative knife's may look pretty but are mostly chrome plated, they do not last long and cannot be sharpened. Make sure the blade is kept razor sharp for cutting, although they can be used fairly blunt (dull) for abrasion.
To blunt a knife running the blade through steel wool will do the trick.

For penetration which im not recommending but if you are going to do then use a much larger knife, perhaps a dagger or sword.
Never insert the blade unless you have a very steady hand, if you are not confident or experienced with a blade then DONT attempt it!

A blade that is 'slightly' sharp is unpredictable and can cause tears rather than cuts or scratches depending on skin texture. Do not use knives with serrated edges or the type designed for food preparation, pocket or Stanley blades.
The use of scissors is also inadvisable. Some experienced Dominants use razor blades (not the cheap disposable variety) or scalpels for cutting.

Razors and scalpels are ideal for creating perfect cuts and patterns but they are much lighter than the blade of a knife and very little pressure is needed,they can be very difficult to judge and should be handled extremely lightly.

When using a razor or scalpel practice on a small area, (the Dominant should test on Him/Herself to gauge the pressure needed, but always bear in mind everyones skin is different, the cut will often appear like a slight scratch to begin with as it can take a shortwhile to open and for the bleeding to begin so wait to see how it develops before re-cutting the same ''wound'' or continuing elsewhere. First timers should not attempt this, and take into consideration that a razor will ALWAYS cut much deeper into the skin no matter how light the pressure.
With a razor or scalpel you will find that the blood takes much longer to surface however do NOT make the mistake of believing the cut is not ''deep enough'' and re-cut.

Always ensure your blade(s) are thoroughly cleaned both before and after use, neat alcohol, a clean soft cloth and mineral oil or liquid dermatological soap are all suitable. Do not steam or place in the dishwasher as hot water will cause both handle and blade to rust. Blood transmits diseases and infections very easily so unless you are playing with a long term partner I would suggest the Dominant wear latex glove's.

The actual letting of blood comes under the classification of blood sports or play but is more commonly known as cutting, therefore negotiation and clarifaction is essential as the term knife play can have very different connotation's for each individual.
State very clearly any boundary's. Always agree a safeword and do not be afraid to use it at any stage, but keep in mind a partial cut does need finishing.

The most common fantasy of playing with knife's is fear and vulnerability, but it can in reality be much more daunting than imagined as I quickly discovered the first time I had a knife held to my throat!Think it through very carefully.

When I first expressed an interest in knife's previously a very hard limit of mine, Icehawk needed to determine exactly what my expectation's were. When discussing all aspect's and different possibility's I realised I hadn't really thought it through very carefully, I just knew the idea of knife play and the sight of the shiny silver sharp edged blade appealed greatly to me
At that stage actual cutting and bleeding seemed pretty heavy and i wasnt yet one hundred percent certain.However he wasnt sure if i'd meant actual bloodletting or not, Hence the need for clear and extensive discussion and clarification.

Firstly handle the knife, feel how with a good quality knife the weight should be equally balanced between the handle and the blade, see that with a good blade even the lightest of pressure can slice very easily and precisely through a sheet of paper.
Try making a slight incision on the back of the hand. You might be surprised that although this creates an open 'wound' there isn't a single drop of blood.
However this can fluctuate, the liklihood of drawing blood can also depend upon body temperature and/or physical well being nothing when it comes to cutting can be certain and you should always take this into account.

My personal preference is cutting with the drawing of blood and marking. If done well the resulting marks last around anything from four weeks to a couple of months sometimes longer depending on age and various skin types, these marks if done neatly can look very decorative.

Marks and scars are a wonderful reminder of a very enjoyable scene or for some a mark of ownership. Permanent marking is for obvious reasons not a decision to be taken lightly. But you should always take into account that for some even the slightest of cuts can leave permenant marks.
I can testify to this, whilst the markages i have were intentional it did not take much to achieve them in fact we were not too sure they would be permenant.
Anyone considering this should seriously think it through and not rush blindly into something irreversible.

For those who find it more difficult to achieve permenant marking careful and precise re-opening of the same wound is the best way to get tround this and some even use ash from cigarettes,although this is something we have not attempted ourselves as yet so i do not feel it would be right to expound on this, although i do know there is no additional risk of infection due to the temperature of the fresh ash.

The Dominant should first practise become accustomed to, and confident with handling a knife, testing upon themselves on different area's of skin, trying different technique's such as scraping slowly downwards with the tip of the blade as when peeling a carrot for example.

Firstly practice upon yourself until you are comfortable and confident practicing upon others,learn how much pressure is needed to pierce the skin with and without drawing blood.

For anyone playing with the intention of cutting and bleeding (not advisable for beginner's) run the tip of the blade gently and slowly downwards as you would do slicing a piece of steak. An important point to remember is not to be afraid to place reasonable pressure on the knife to enable it to do its job properly.

Despite my warnings (though please take them seriously) most cutting's will not leave permanent scarring and it can actually be quite difficult to achieve due to the skins natural resilience and healing process. Slightly jagged uneven cuts are less likely to scar.
Thin skinned areas such as above a bone are more prone to scarring than skin on fleshier area's like the thighs stomach or buttocks. Keep in mind that although rare, some people with even the slightest of scratches or incision's can be left with permanent marks. If the risk of scarring is unacceptable to you be extremely cautious when considering cutting.Planned or not scarring is always a possible outcome.

Do not use on the neck or face and stay well clear of skin close to veins and arteries, for example the wrists and inner arms. Take your time prolong and enjoy the experience it does not need to be overly clinical unless of course that is your intention. Just use your common sense and take all the necessary precautions.
Maintain a high standard of cleanliness at all times,gauze,bandages ,sterilized wipes and ointments such as savlon are always handy to have close by. It's rare and dont be put off but always keep in mind accidents can and do happen after all you are playing with a dangerous implement. If the worst should ever happen and the wound needs attending to then do not be afraid to go straight to the nearest A&E department,much better to face embarrasment than any possible after effects.

Any pain from the use of knife's is fairly minimal usually a scratching sensation when used for abrasion or when cutting a stinging feeling not unlike a paper cut,razors and scalpels more so. Using knife's for the sole purpose of giving or receiving high levels of pain despite what some may claim is not the case and atempting it is definitely not recommended.

Little aftercare should be needed, keep the wound's/ abrasion's clean (soap and water is fine) and as mentioned previously make sure your knife is always in pristine condition and never used for any other purpose.

Lastly if any of the parties involved is not comfortable then say so immediately and stop!