Subcontracting blasting

[Robert Schwieger]

I am undertaking a larger glass project for which I lack the proper tools to prepare the glass for chipping. I have been reasonably successful on smaller projects but simply don't have suitable work space to accommodate the larger glass for blasting. I know that it is risky subcontracting the initial frosting but I would like to know what I should expect from the subcontrator such as the appropriate abrasive (sand, aluminum oxide, etc) and stencil material. SInce my work has been hand cut stencils and using contact paper and aluminum oxide (220) what should I request from the subcontractor.
I know this would be risky but it may be my only way of accomplishing this project. Your wisdom will guide me here. Thank you.

[Mike Jackson]

A: Make small samples for them to blast before you let them do the big one.
B: Make more small samples for them to blast before you let them do the big one.

C: If in doubt, use regular sandblast stencil and not contact paper.

Mike Jackson

[Larry White]

Hi Robert-
You might find yourself in the position of asking the subcontractor what they can supply to you, rather than being able to dictate to them what you want. My first question would be if they've ever sandblasted glass before, and, are they familiar with the appropriate handling methods on large glass (although your idea of large, and my idea of large, may be two different things). I would seriously avoid the contact paper and use a proper sandblast resist. I like to use Venture tape 4 mil white vinyl sandblast resist for most surface etching applications. It just seems too risky having someone that may be inexperianced sandblast it with contact paper. I would ask them to blast it with their finest sandblast medium, and at a low to moderate pressure, emphasising that you just want the glass frosted. You might also want to consider masking the face of the glass to avoid it getting scratched during the handling. And ya, like Mike said, do a sample first! Hope that helps.

-Larry

[Doug Bernhardt]

Robert......I have been subcontracting my blasting since always. I go to a glass shop (stained glass etc) and they have been perfect since the first time. They're now also friends (sorta). They'll drop what they are doing whenever possible for me, we share ideas and it's always great to see what they are doing. The same interest is shown in what I'm busy with and it's a perfect relationship. Never even had a discussion about money as it's always been incredibly reasonable.

[David Slade]

Just curious...
Has chipped glass always been prepped by sand blasting? Or, did the old-timers have some other method of roughing up the surface?

[erik winkler]

Yes I read that they used emery powder to rough the glass.
This was done with a glass plate rubbing the emery powder on the working glass.

Erik

[Doug Bernhardt]

I have an old "signs of the times" in which someone has a question about "spangled glass" and it is described how they use HF to break the surface in preparation. It as well as the whole magazine is fascinating reading. It was similar to a question and answer column in today's mags.

[David Slade]

Thanks Erik and Doug!

But.. What's HF?

[Danny Baronian]

Hi David,

HF: Hydrofluoric Acid.

Wiki definition:

Hydrofluoric acid is best known to the public for its ability to dissolve glass by reacting with SiO2 (silicon dioxide), the major component of most glass, to form silicon tetrafluoride gas and hexafluorosilicic acid.

Also used in toning glass acid etching and acid embossing.

Danny

[Robert Schwieger]

Hello again,

What are the pros and cons of silicon carbide as the abrasive to prepare the glass for chipping. A local stained glass artist uses this in his etch work and will do the subcontracting. Bob

[Doug Bernhardt]

Am sure there are more pros than the fact that everyone uses it and the only con I know of is getting the glass cleaned of it prior to silvering. Smitty has a good method rather than my scrubbing away with a dissolved lye bath. Ooops......sorry for the short hand guys.

[Danny Baronian]

You'll have to forgive Doug. His brain, like our hard drives sometimes get over worked, or over loaded. That's probably the case here as he's so busy these days .

Re: Silicon carbide - pros: cuts fast. As particles break down, they form new sharp edges that will continue the cycle during blasting / re use until the material has disapated. Does not require special clean up other than cleaning as normal for silvering. Cons: expensive. But I've found Silicon carbide will outlast aluminimum oxide 5 to 6 times longer.

ALUMINIMUM OXIDE: Pros: inexpensive. Cons: Requires a lye bath to remove alinimum that will contaminate solutions when silvering.

Note to Doug: If you're using Silicon Carbide and using lye to clean the glass, skip the lye and clean as normal. If your using Aluminum Oxide, continue with the lye treatment ...... Whatever you're doing, the end results look good!

[Doug Bernhardt]

Apologies Danno......As you CAN see, I DON'T do the blasting so my mistake. Aluminum oxide is what they use.....and I clean heartily!!