Cold Knife Blades

In the last post, I talked about the proper use of the cold knife in terms of positioning, leverage and effort.  Today I want to address the most important part of the cold knife – the blades.  There are a number of different types, sizes and configurations that I wish to address because they all have a purpose.

Before I begin, I have one more comment on the cold knife that needs to be mentioned in relation to the blades.  There are so many options for cold knife blades that taking advantage of their benefits requires that a “fast blade change” knife is highly recommended.  Those that do not take advantage of fast change knifes have a tendency to use the same blade over and over and miss the advantage of multiple blade options.  So, consider one of the numerous fast change knives available or buy several common knives with various blades installed.

The original or standard cold knife blade was designed for the less problematic adhesives of yesteryear.  It had a dull point at the tip and parallel sides and it had several blade lengths for ease of cut out. The insertion into the adhesive was no problem because the adhesives (Butyl and Polysulfide) were not as hard or dense as urethane.  The benefit of the standard blade was the durability.  It could be sharpened many times and when it weakened it bent instead of breaking suddenly.  It did serve our industry well for many years.

One of the most popular cold knife blades that have been introduced in the industry is the wizard blade made popular by the Ultra Wiz brand.  The popularity is from the design of the blade.  It is sharp and pointed at the tip for easy puncture into the hard urethane and tapers wider at the base for strength during the cut out.  However, what makes this blade easy to insert also makes it harder to control.  The taper of the blade actually causes the blade to move outward toward the wall of the pinchweld if not controlled.  It becomes necessary to pay attention and hold the knife into position for an easy and damage free cut out.  For most experienced technicians this is second nature and not a concern because they learned how to use a wizard blade when the gap between the glass and the pinchweld was enough to allow for mistakes.   Then when they mastered their tool they also mastered the blade action.  This is not as easy with the close tolerance designs of today.  The new tech must control the knife to keep the vertical leg of the blade as close to the glass edge as possible or damage to the paint is inevitable.

To counter the natural action of the blade’s movement and to address the close tolerances of glass to body in modern vehicles, most blade manufactures came out with coated or padded blades.  The coating or pad was added to the back side of the vertical leg of the blade which is where the blade would make contact with the wall of the pinchweld.  It works quite well but the coating or pad would wear off quickly and then the special blade would be made common.

There has, over the years, been many different blade innovations introduced, some successful and others not so successful.  Here are some that I have seen and had the opportunity to have tried out.  I think you all owe it to yourself to try them out.  You may find a product that will make you jobs easier and faster.

  • Different Lengths of Blades – When it is hard to cut out, start with the shortest and move up incrementally to the longest until the glass is released from the adhesive.  There is usually a short, standard and long in all of the styles following.


  • Molding Saver Blades – Unique bend

  • Stainless Steel Blades – Harder material for long lasting edge

  • Scratch Resistant Blades – For use on close tolerance parts and paint protection

  • Interior Removal Blades – Use for interior cut outs

  • Reverse Bend Blades – The flat blade surface is to the pinchweld instead of to the glass.  This causes the blade to cut closer to the metal instead of shaving the urethane from the underside glass surface.

  • Coined Blades – This means hardened and thinner.


  • Serrated Blades – The underside of the blade is serrated instead of flat and the entire blade is thinner.

Some may say that all these new blades styles are simply trying to invent a new “mouse trap” and, in a sense, they are.  The common theme in all these blade styles is to make your job easier, faster or cheaper and, in most cases, I think they do a good job in doing just that.