February 6, 2010 at 5:36 pm

Solutions for PhotoResist Blow Outs

Often times people have problems with there photoresist stencil blowing off while sandblasting.  This is a fairly common problem the arises.  It doesn’t seem to happen as much with a regular vinyl stencil but does every once in awhile. 

A fellow glass sandblaster, named John, emailed me about this problem and here is my response with a bullet list of rules and actions to consider.

  1. Use a Finer Abrasive Grit:  There could be a few things to consider, but the one that comes to mind is that the grit being used is too large.  I personally use about 150 or 180 grit.  I probably wouldn’t use anything larger in size than 100 grit (but my grit standards are set at least 120 and finer).  Sometimes they don’t emphasis this enough, but the finer the grit is, the less blow off problems you will usually have and the thinner the vinyl stencil can be.  I talked about that in the ebook a little bit also.  Alot of times, I will actually do some sandcarving with a 3 mil vinyl with a fine grit.  Works fairly nice.  By the way here is some more steps to follow for glass sandcarving.
  2. Ensure a Clean Surface:  Another problem could be due to having a unclean surface.  Even if the glass appears to look very clean, it still has oils and such from peoples hands.  You can wipe the glass down with a cleaner such as rubbing alcohol.
  3. Dry Out the Resist, but not to Dry:  A third, is to make sure that the photoresist is dry but not bone dry.  I use the photoresist that doesn’t require an application of adhesive.  Its most tacky when it is almost dry.  If the photoresist still has moisture absorbed, then the photoresist won’t adhere very well.
  4. Lower the Air Pressure:  A fourth rule, is to make sure the sandblasting pressure isn’t set at too high of a pressure.  The photoresist company will usually have a recommended and maximum pressure that can be used for each specific photoreist thickness.  Then it will also go back to the first rule I stated.  If a larger grit is used, you may have to back off the pressure too.

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2 comments so far

  1. Jason

    March 12th, 2010 at 2:29 pm

    Good summary, it triggers two questions for me.
    1. what photoresist do you use?
    2. what is the threshold for “blow-through”, instead of blowoffs. Meaning, how much pressure and large grit sand can I use before I blow through the protective layer?

  2. Eric Robert

    March 12th, 2010 at 3:25 pm

    Hi Jason, I have been using Rayzist photoresist, but I am sure the others such as Photobrasives brand work just as well. I hear both are quality brands.

    I assume your second question only pertains to the blow through of the light protective layer or the residue over the areas that need to be blasted (exposed areas) and not the actual stencil areas. I am not sure about the exact pressure and grit combination to blast through would be. It should be able to blast through at any pressure which would etch the glass. My guess would be 10-15 psi could blast through at a typical grit used such as 150 grit. Maybe I’ll test that for you. But even if you have a fine grit or a low pressure it might blast through but at a much slower rate. It could still blast through but with longer blasting time.

    I assume your using a small airbrush sandblaster. Best bet would be to ask the photoresist company. I’ll try and test a low pressure setting one of these times. I hope that helps.

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