A ceramic knife blade is made out of a material that is so hard that only diamond is harder. That material is usually zirconium dioxide (ZrO2) also known as zirconia. These blades are produced by pressing zirconia powder under high pressure and firing them through a computer controlled sintering process that takes several days. The blade that is produced is sharpened by grinding the edges with a diamond-dust-coated grinding wheel.
To make this blade tough and not too brittle, it is produced by the addition of 3% mol yttrium oxide yielding partially stabilized zirconia. This causes a structural change in the zirconia allowing for a much tougher material.
Several brands on the market now have a black colored blade which is made through an additional 'hot isostatic pressing' (HIP) step, which improves the toughness.
Ceramic vs Metal
The only real difference here is the blade material. The blade is the most important part of the knife and with that you have a major difference in a metal blade and a ceramic blade. So what happens when you compare these two materials? You get pros and cons to be sure.
The ceramic material is very dense which means it has a low porosity. This is good for not transferring tastes from other foods. Just rinse under warm water and your blade will be cleaner than if you scrub your metal knife.
Ceramic material is so hard that only diamond is harder. This means that your edge will stay sharp for year's vs weeks or months for a metal edged blade. Most ceramic blade manufacturers will even sharpen your knife for free due to low number of times it might be needed. Manufactures of metal blades will never offer this service due to the amount of times it would need to be done.
Ceramic material is very light and thus you can wield the knife for a lot longer with less strain on your hand and arm.
And finally, no metal, no rust or pitting or rolling of the edge leading to a dull blade.
Being extremely hard does not mean that this blade is not breakable. Ceramic blades are not meant to cut frozen foods, bones or anything else that is not easily sliced. The tip and cutting edge of these blades can be easily chipped and great care should be taken in ensuring that they are not brought into contact with anything hard.
The cost of these knives is really in line with high end metal knives. Due to the high cost of manufacture you will not find a low cost version of this type of knife which makes it seem expensive.
It's not the most versatile blade in the kitchen but if used for what it is intended, slicing, then you will have a great addition to your knife collection. If you need to cut bones or frozen whatever, use a butcher knife!
Is It Worth The Price
You can buy very high quality ceramic knives for less than a $100. Shopping around for a very high quality metal blade knife and you will pay upwards of $300 or more. As stated above, there is a long and costly manufacturing process and you will not find a cheap knife at Wal-Mart. If you look online you might find some ceramic blades on sale for the smaller paring knives that you might be able to get for $20-$30.
It is also not recommended that you put these knives into a dishwasher. The hard spraying of the water and movement of dishes can cause the blade to come into contact with a hard object like a plate or glass bowl causing it to chip.
The bottom line is if you need a knife to cut veggies and fruit or a blade to cut meat then there is not a better product out there.