DIY Contact Print Frame - Glass?

[MurrayMinchin]

Hi there,

I'm considering using a heavy sheet of glass for a contact printing frame rather than having pressure springs on the frames back. It'll be used for salt prints and/or kallitype's.

I seem to remember reading that 'lead free' glass doesn't absorb a lot of UV light...is that right? Also, are there other types of glass which come highly recommended for transmitting UV light?

Thanks a bunch.

 

[fgorga]

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.

 

[MurrayMinchin]

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.

Thanks for that. Was hoping someone might have jumped this hurdle already.

I'm planning on getting a small device for measuring accumulated UV light during exposures, so I could get some glass samples from local shops and test which one lets the most UV through by giving each one the same exposure.

 

[DMJ]

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/

 

[MurrayMinchin]

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/

Sounds promising, and heavy!

While I am inclined to try DIY projects, electronic gizmos are totally out. I was thinking about: http://www.lightmeasure.com

 

[DMJ]

It's a 16x12 1/2in glass and weights 6.5lb. For larger cyanotype prints from plants sometimes I use the glass from a garden table that is 1/2in thick and measures 36x44in, That one is heavy!

That is a nice device and they ship from CA