DIY Contact Print Frame - Glass?

fgorga said:

It is hard to give you a precise answer because there are too many unknowns.

The UV absorption of glass is dependent on the wavelength and drops off rapidly below 320 mm. But even above that number, there is significant absorption of light until you get to the visible. Since we don't know the exact wavelengths involved in most alt processes, we can't really say how bad the absorption will be

Also remember the thicker the glass the more the radiation will be absorbed. This is a linear process... double the thickness of the glass and the tranmission of light will fall by a factor of two.

Thus, the best advise I can provide is buy a piece of glass and experiment... see if you get exposure times that work for you.

On occasion, I will improvise a contact printing frame using an oversize piece of regular 1/8 inch (3 mm) window glass weighted on each end with bricks (work best) or stones (if I am really improvising) rather than using a thicker piece of glass. I do this when I need a few extra setups and don't have enough regular frames, or when I want to make a larger than usual print... i.e. these are meant as temporary solutions. I use this approach most often when making photographs rather than when printing negatives

I tape the edges of the glass with masking tape because the edges are quite sharp.

Regular window glass is very easy to source and inexpensive.Most hardware stores carry window glass while to get thicker glass generally requires a visit to a specialist supplier.

Exposure times with window glass are similar to those with my regular contact printing frame.

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DMJ said:

I use a 3/4in piece of glass that I ordered custom cut at the local window shop in my neighborhood. I asked for a non UV blocking glass and I can do kallitypes in 4 minutes with my light source and DNs. It works for me.

What UV measuring device are you planning on getting?

There is one DIY device linked here under Blogs. It uses an Arduino microcontroller.
https://apenasimagens.com/en/solar-uv-exposure-meter-complete-project/

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