All About Contact Printing Glass

[Mat23]

Howdy Alll,

I'm going to be making some largish prints 27x34cm quite soon, cyanotypes & VDB. They will be contact printed with a homemade UV tube box under glass only (not using a bespoke frame) using a digital negative on to Platinum rag.

Before I buy a sheet of glass, I want to check the glass spec.

From previous posts there is nothing to suggest any advantage in spending more money on super clear low iron glass as opposed to regular plate glass apart from marginal faster exposure to times.
I am fine with this.

However, the spec I would most like to confirm is the glass thickness. My concern would be Newton rings therefore something of suitable weight for full digital negative contact. 10mm too light?

A supplementary question would be do you use or think that a felt board under the rag would assist with delivering the best contact posdible?

Cheers People.
Mat

 

[cliveh]

I would suggest you use thick plate glass that has a crack in it. That way you will get a variation of refraction that is unique to your images. Look at some of the images produced by Sudek.

 

[Mat23]

I would suggest you use thick plate glass that has a crack in it. That way you will get a variation of refraction that is unique to your images. Look at some of the images produced by Sudek.

Cheers Clive,

A random but great idea. Probably not for this particular portfolio but you never know!

Best regards
Mat

 

[awty]

I use 1/4"/ 6mm glass on my home made compact print frames. Biggest will do 14"x17". As long as the compression is even as you can make it you shouldn't have a problem. Thicker glass may prevent some UV from getting through and thinner glass may have un even compression and or break.
Make sure you back the paper side with thin felt. I like to use a bit of thin card on larger prints as well to make sure compression is even where the hinge back is.

 

[Dan Pavel]

I made a high-compression A3 contact-print frame out of Al. square profiles and first I used an 0.5mm glass on it, but it didn't resist. I replaced it with 1cm glass and now it is O.K. I haven't noticed any problem with longer exposure times - probably they are a bit longer, but not significantly longer. What I have noticed was a clear improvement in the prints details due to the higher pressure. Another bonus of the high-pressure contact-print frame is that I can use it as a handy paper press, as well.

 

[Mat23]

I use 1/4"/ 6mm glass on my home made compact print frames. Biggest will do 14"x17". As long as the compression is even as you can make it you shouldn't have a problem. Thicker glass may prevent some UV from getting through and thinner glass may have un even compression and or break.
Make sure you back the paper side with thin felt. I like to use a bit of thin card on larger prints as well to make sure compression is even where the hinge back is.

Thanks Awty, I forgot to say that I'm not using a printing frame, glass only, how does this change your advice? Cheers

 

[Mat23]

I made a high-compression A3 contact-print frame out of Al. square profiles and first I used an 0.5mm glass on it, but it didn't resist. I replaced it with 1cm glass and now it is O.K. I haven't noticed any problem with longer exposure times - probably they are a bit longer, but not significantly longer. What I have noticed was a clear improvement in the prints details due to the higher pressure. Another bonus of the high-pressure contact-print frame is that I can use it as a handy paper press, as well.

Howdy Dan, I forgot to say that I'm not using a frame, just glass, any advice, cheers! Mat

 

[awty]

Thanks Awty, I forgot to say that I'm not using a printing frame, glass only, how does this change your advice? Cheers

No difference, the weight of 1/4 glass is enough to hold the negative to the emulsion paper. I use this method for silver gelatine contact print under the enlarger.
I use a compression frame for sun exposures so I can point the print to the sun.

 

[Mat23]

No difference, the weight of 1/4 glass is enough to hold the negative to the emulsion paper. I use this method for silver gelatine contact print under the enlarger.
I use a compression frame for sun exposures so I can point the print to the sun.

Thanks Awty got it, you use 6mm regular plate glass successfully without additional compression or a frame on a digital neg up to a max size of 14'x17' without issue from rings. Additional felt is noted. Many thanks.

 

[awty]

Only time I see newton rings is with uneven compression while using a contact print compression frame.

 

[koraks]

I replaced it with 1cm glass and now it is O.K.

Holy cr*p, that's one heavy frame you built there. I use 5mm in a similarly sized (well, slightly bigger) frame and that's about as heavy as I'd want to make it.

Btw, I see no difference in exposures between the 1mm cheap picture frame glass of my small printing frame and the 5mm glass of the bigger frame. Prints at the same speed. Plain float glass without any coatings or otherwise special specs is perfectly OK for contact printing with alt processes.