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screen printing => Screen Making => Topic started by: cvreeland on January 16, 2013, 05:31:55 PM

Title: "Stir with non-metallic paddle" Why?
Post by: cvreeland on January 16, 2013, 05:31:55 PM

This is a thing that's never been explained to me. All diazo emulsions will ship with the little bottle of sensitizer & the instructions for 20 years have said to use a non-metallic paddle or stir stick to stir the sensitizer in to the photo emulsion.

But... as soon as the bubbles settle, we're all pouring it into a metallic scoop coater. I've used a stainless steel spatula to stir my emulsion for years, and if there's been a problem, then I do't know what it is.

Why do emulsion manufacturers still put that in the instructions? What bad thing is supposed to happen if we use a metallic stirrer?

Just one of those little questions in life...

Title: Re: "Stir with non-metallic paddle" Why?
Post by: jsheridan on January 18, 2013, 10:33:36 AM

Diazo is an acid base.

combined with water and metal, it can oxidize. It does tarnish those steel blades over time.

Title: Re: "Stir with non-metallic paddle" Why?
Post by: tonypep on January 18, 2013, 10:38:45 AM

Correct. It's why most come with a wooden paint stirrer

Title: Re: "Stir with non-metallic paddle" Why?
Post by: cvreeland on January 18, 2013, 07:47:15 PM

Quote from: jsheridan on January 18, 2013, 10:33:36 AM

It does tarnish those steel blades over time.

The horror!  :P

Discharge is a lot worse on my spatulas than emulsion.