We had a recent post on schlieren photography (it is useful to read that post to understand this one). One of the components used to make the photographs was the blade from a utility knife used to block light that only passes through air of ambient temperature.
This worked but I realized that the lower portion of the blade was blocking too much of the non-refracted light. I replaced the utility knife blade with an Exacto knife blade to see if that would improve my images.
To compare the results, I examined images of the same object (the output of a woman’s hairdryer) before and after the change. This is the image using the utility knife blade.
This is the corresponding image using the Exacto knife blade.
This is a significant improvement. Other images can be seen in my flickr account.