Flaws of Double Slit Experiment? The double slit experiment usually use knife blades for the slit.
But knife blades are made of metal and they are highly reflective for light rays.
This means the incident light should reflect off the tip of the blade and create unnecessary interference.  
As shown in the image below:  
 
Has this effect been properly prevented by using a non-reflective surface such as "Vantablack" for the slit?
https://en.wikipedia.org/wiki/Vantablack 
Is the current double slit experiment flawed?
Or do they have a way to prevent this effect?
 A: In the classical electrodynamics doubles slits experiment , reflection and refraction of light at the edges hit play a role in creating the pattern. If the light goes through without interacting with the slits there is no interference. That is why the distance between the slits and the size of the slits  with respect to the wavelength under study is important. The slit has to be small enough so that it becomes a point source, the refracting part of the wave off the straight incoming path giving rise to interference.
The same is true for the quantum mechanical view of photons, for light, and electrons, where they have a quantum mechanical probability distribution impinging on the two slits, solved by the boundary value problem " particle falling on two slits of given width and separation" , which will give a wavefunction, which complex conjugate squared gives the interference pattern, even one photon at a time.


Single-photon camera recording of photons from a double slit illuminated by very weak laser light. Left to right: single frame, superposition of 200, 1’000, and 500’000 frames.

What you call "unnecessary interference" is a necessary part of the explanation of the interference both classically and quantum mechanically. This answer for electrons is relevant to the discussion.
A: Of course this has been done: scratches on a sooted glass plate. It is the standard set-up in the course lab, for example:
https://www.pasco.com/products/lab-apparatus/light-and-optics/diffraction/os-8453
The slits can be made by a photographic process. Or by printing in a laser printer, using toner on a transparency: Van Hook, Inquiry with Laser Printer Diffraction Gratings, The Physics Teacher 45, 340 (2007).
