SPI Supplies offers three different types of diamond knives (life science, materials science, light microscopy/histology) and six different boat styles. For most ultramicrotomy applications the standard life science diamond knife in the standard boat (Style S) is the preferred combination. For those cutting hard materials, be they hard because they are hard materials science samples, or hard because they are hard tissue materials such as bone, teeth, or cartilage, the SPI Supplies materials science knives should be selected. For work at the LM level, the "light microscopy" knife should be selected. And for some very specific applications, such as cryo sectioning, one might want to select a diamond knife and boat designed specifically for that application.

The two main parameters are A) knife length and B) knife angle. The price is primarily determined by the knife edge length, not by the angle or the style of the boat. For some years SPI has been working with some of the leading suppliers in the diamond area, and we offer a total of seven different diamond types covering virtually the entire range of diamond knife applications. If you are doing ultramicrotomy we have one diamond type that is optimum. If you are doing light microscopy there is a diamond optimum for that application which is different from the first application.

Each of the seven different knife types is produced in a variety of different edge lengths and also a variety of different knife angles. The table below outlines the full range of the choices. There are two angles important in selection and using diamond knives, the included angle and the clearance angle.

The included angle is measured between the two facets that form the knife edge. The standard included angle in SPI Supplies diamond knives is 45° which is what is used for routine sectioning. Optional angles are 35° and 55°. Or just about any other angle desired can be special ordered with no additional cost. Just tell us your needs and we can usually produce just about anything needed.

A 35° included angle is the angel of choice when any kind of deformation (e.g. compression effects) must be kept to a minimum. A good example would be those researchers needing the very highest quality of a result. However, like with everything else in life, with diamond knives, there are also trade-offs. The lower angle, in addition to making the edge far more fragile, also results in a noticeably faster wear rate, meaning that the knife will have to be resharpened more quickly. The larger angle 55° is recommended when one is sectioning the very hardest of materials and they want to have longer knife longevities. However, as the angle becomes more and more "blunt"one also experiences more distortion and compression effects, often times even leading to an over all inability to cut samples with 55° edges that could be easily cut with 45° edges.

One final comment and that is that at times, certain hard materials that can not be cut with a 45° included angle can be cut with a 35° knife. However, again it is a matter of trading off since the 35° will surely wear out very quickly. However, for some really important and high priority samples, that price might not be too high to pay in order to get any results at all, especially if one is contemplating the use, to study the sections, on a $500,000 to $1,000,000 instruments!

The clearance angle is the angle between the back diamond facet and the block face in the ultramicrotome. SPI Supplies diamond knives, as a consequence of the use of the new laser alignment technology, exhibit perfect alignment with the back plane of the boat. The actual clearance angle during sectioning, therefore, is the angle actually called for on the ultramicrotome angle setting. The suggested clearance angle, for optimum results, is usually 4° or 6°, and is indicated on the name plate on the knife and also on the quality certificate. One can use clearance angles outside of this stated range, in order to realize a broader range of sectioning conditions, however, for angles larger than 10° we would urge caution since such an angle could result in excessive stress on the edge, thereby damaging it beyond repair. Angles less than 2° would similarly be not advised because of the danger of the knife rubbing against the block face resulting in uncontrollable knife "chatter".

The angles given represent "stock" angles available from SPI. This is the "default" angle that is shipped absent any further instruction from the customer. The other stated angles are essentially "stock" angles that are available should they be requested by the customer. Other angles are possible, and we will supply just about any angle, however it is important to specify the angle if one other than the "default" angle is desired. The default angle is always in bold face (e.g. 45 deg.), just to make sure that the customer knows that this is the angle that will arrive if no other angle is specified. The default angle is selected to coincide with the one angle most often requested for a particular type of diamond and for a particular application.

The table also contains information about the range of selection thickness generally possible with a particular type of diamond(e.g. length and angle). Each knife is tested by cutting sections at specific thicknesses and examining them at particular magnifications. These conditions are indicated on the Certificate of Quality which is provided with each knife.

From this information and also the information under "applications" everyone can identify which diamond will be optimum for their samples.

Note: The selection of the "right" diamond is just the first of a two part process, since after selecting the diamond, you will have to select the optimum boat.

SELECTION OF THE DIAMOND                                    

TYPE	AVAILABLE EDGE LENGTHS (mm)	AVAILABLE INCLUDED ANGLES(Deg.)	RANGE OF EXPECTED SECTION THICKNESS	APPLICATIONS
SU	1-6 mm	35,45,55	25-200nm	Standard ultramicrotomy and sectioning of biological specimens and materials
CW	1-6 mm	35,45	50nm-1um	Frozen specimens sectioned wet like with ethylene glycol
CD	1-6 mm	35,45	50nm-1un	Frozen specimens sectioned dry
TS	1-6 mm	45,55	50nm-2um	Thick sections, or alternating thick/thin sections
MT	2-7 mm	45,55	50nm-2um	Materials science plastics, catalysts, other hard samples.  Also can be used for hard tissue materials such as bone, cartilage, teeth, chitin containing or hydroxyapatite containing samples.
LC	4-7 mm	45,55	0.1-5um	Frozen specimens to be examined by LM. Recommended cryo boat styles D or W.
LH	4-10mm	45,55	0.1-5um	Sections to be examined by LM.

Selection of the Boat

Boat Style S: Standard boat with oval cavity.  Black anodized.  All  new knives, except cryo and knives larger than 7mm are supplies in this  boat, unless otherwise suggested.
Boat Style W: For wet cryo sectioning.  Made of stainless steel  with no glare finish and cylindrical cavity.  6 deg. inclined top.
Boat Style D: For Dry cryo sectioning.  Stainless steel non glare  finish.
Boat Style H: Cylindrical cavity, 6 deg. inclined top.  Available  in black or non glare gold anodizing.
Boat Style M: Wide oval cavity boat, black  anodized.
Boat Style P: Large Boat with oval cavity and 6 deg. inclined top,  black anodized.  Supplied with knives 7mm and larger or per request.