Replacing or sticking together complete although broken pieces of glass

[Enrique Laks]

In Costa Rica we have restored many Catholic churches' stained glass windows made in Europe, some of them more than a century ago, painted by that time's finest artists. We found that between 40% and up to 70% of those windows' glass was either missing or broken. We replaced every single piece of glass. We did our best to find out the artists' methods, the glass, the pigments, the mediums they used and we made every effort possible to have the replaced pieces look exactly the way the original artist did his work. We also replaced, making them anew, every piece of glass that was complete although broken.
Question: is it convenient and accepted by restoration standards to stick together those complete but broken pieces of glass? Or is it better to replace them with new glass painted like the original pieces? How long those sticked together pieces would last before the crack starts showing again?
Enrique

[Vic Rothman]

In Costa Rica we have restored many Catholic churches' stained glass windows made in Europe, some of them more than a century ago, painted by that time's finest artists. We found that between 40% and up to 70% of those windows' glass was either missing or broken. We replaced every single piece of glass. We did our best to find out the artists' methods, the glass, the pigments, the mediums they used and we made every effort possible to have the replaced pieces look exactly the way the original artist did his work. We also replaced, making them anew, every piece of glass that was complete although broken.
Question: is it convenient and accepted by restoration standards to stick together those complete but broken pieces of glass? Or is it better to replace them with new glass painted like the original pieces? How long those sticked together pieces would last before the crack starts showing again?
Enrique

While I can not speak for everyone. I would think that the majority of "conservators" whether they work in stained glass,furniture, painting or buildings would attempt to keep as much original material as possible. That would mean that gluing broken glass is the way they would do it.
They have been gluing broken glass all around the world for over 30 years now. How long it will last would depend on many different factors such as protection glazing, venting, the glue used, the ability of the conservator.

[glassheritage]

while we do use both the renforced copper foil method and hyxtal gluing ... Vic is correct, it is always best to preserve as much of (if not all) the historic fabric of the original glass ... we base our decision to replace on the damage done to each individual piece ... if we can glue and infill with a minimum amount of visibility, we glue ... if gluing is not an option, we copper foil ... if the window has great historic value we may plate ... if the glass is missing, or the is too far gone (many breaks or missing broken pieces), we will replace it ...

hope this helps

[Enrique Laks]

We thank you Vic and John for your enlightening comments.  We agree that it is always best to preserve as much as possible, restoration should be only part of a broader concept: CONSERVATION. For our restoration work we have followed the concepts of a book written in 1993 by Julie L. Sloan: Conservation of Stained Glass in America, a Manual for Studios and Caretakers (Art in Architecture Press) which we found very adequate. She mentions several methods for mending glass, such as lead insertions, copper foiling and edge-joining. We made lead insertions and copper foiling several times, but only when the glass was large enough and the mending was done at a side and it did not change the piece. We have also given many thoughts to  possibly seaming together with glue the two parts of a glass that broke with a clean crack but we never tried it, we feared it would not last much time. How reliable you feel the hyxtal glue is nowadays, when applied correctly?
What about restoring a broken piece of glass when parts of it are missing? If you say infilling with a minimum amount of visibility, how to decide where is that minimum?
I think it would be a great exercise for many studios to be informed of other studio?s opinions on important matters like this one and present their own opinions. Such an exchange might give new lights to many of us.     

[Enrique Laks]

A question for Vic and John; as well as for any glass restoration expert that might be interested in this subject:

Is HXTAL NYL-1 the best glass adhesive available today, as its manufacturer claims to be?

[Vic Rothman]

A question for Vic and John; as well as for any glass restoration expert that might be interested in this subject:

Is HXTAL NYL-1 the best glass adhesive available today, as its manufacturer claims to be?

YES

[Enrique Laks]

Thank you for the information Vic, we appreciate it. We will start learning how to use HXTAL NYL-1 as an alternative process and apply it at our next restoration projects whenever the situation of any cracked glass would deem it convenient.
Enrique

[glassheritage]

yes, hyxtal is best ... for repair of pieces missing some glass, we, at that point, in consultation with the client, we cut a new piece for total replacement ... if painted it is imperitive that the piece base glass and paint be a match, or it will stick out like a sore thumb ...

[Enrique Laks]

Thank you John for your comments confirming hyxtal is best. If it is a clean crack, how about the union of the two broken parts, how much does it show? Is it possible to hide it completely so the crack is not noticed? We agree that preserving the original piece is better, as long as the crack is perfectly hidden and ir does nor show. It is certainly easier and less expensive to glue than to replace but it is still a difficult decision for us, we are not sure the crack can become invisible, how do you feel about that? Also, if the glue could perfectly hide it, for how long?

[Vic Rothman]

Thank you John for your comments confirming hyxtal is best. If it is a clean crack, how about the union of the two broken parts, how much does it show? Is it possible to hide it completely so the crack is not noticed? We agree that preserving the original piece is better, as long as the crack is perfectly hidden and ir does nor show. It is certainly easier and less expensive to glue than to replace but it is still a difficult decision for us, we are not sure the crack can become invisible, how do you feel about that? Also, if the glue could perfectly hide it, for how long?

Totally invisible never happens. At the very least you can see a line where the glass is joined if you get up close and look. With opal glass it's hard to see. With more transparent glass it all depends on the light refraction index  of the glass and that of the glue. The closer the number the more the break disappears. There is another good glass epoxy called Epotek 301-2. The refractive index is slightly different then Hxtal, so in some cases the break is harder to see.
It's not a question of how long a repair will last. In important windows it's more important to save the original material, even if you need to keep on repairing it over time.

[glassheritage]

I agree with Vic, the crack is never 'perfectly hidden' ... I am not familiar with the adhesive he recommends, and will be trying it out soon ... always saving the historic fabric of any window should be of paramount importance ...

[Rebecca]

I agree with Vic, the crack is never 'perfectly hidden' ... I am not familiar with the adhesive he recommends, and will be trying it out soon ... always saving the historic fabric of any window should be of paramount importance ...

For this reason, if a piece of glass is broken with a shard missing, I use Hxtal to repair it, not cut a new piece.  A matching piece of glass can be cut and painted and glued in place of the shard with Hxtal, or the missing space can be filled with tinted Hxtal and cold painted if necessary.

Rebecca

[Enrique Laks]

We agree that saving the historic fabric of a window is of paramount importance, but how to decide where to draw a line if a piece of glass is broken in more than two parts or if more than one shard is missing? What tells you that the time has come for a new piece to be cut to replace the original?

[John]

It comes down to your judgement.  Can you make the glued piece at least match the quality of the rest of the window?  If the rest of the window has dozens of replacement pieces, or dozens of lead dutchmans, that might lead to a different decision than if the window were otherwise perfect.  Does the piece have heavy painting on it?  Can you glue the piece, fill the missing shard with Hxtal, and use a cold paint (like a non-fired enamel) to conceal the missing paint?  Is the repair going to be viewed close up at eye level, or will it be 40 feet off the ground in a busy window where no one will ever perceive it?  Is the broken piece a too-thin piece of glass right behind a rebar that will probably rebreak the next time a strong wind pushes the panel from the exterior?  Maybe you should just lead the two pieces to reduce the risk that the glued piece will break in a new place.  Does the broken piece provide structural protection/support for a more valuable piece of adjacent glass?    Perhaps you should replace it with a thicker piece to protect the more valuable piece next to it. 

Those are just some of the non-artistic considerations. Remember that large windows usually represent the work of multiple artists of different abilities.  Novice glass painters spent their hours churning out border pieces.  More experienced painters were put to work mass producing more technically challenging pieces, and the master painters painted flesh and the extremely artistically expressive and difficult pieces.  Is the piece apprentice-grade work, like a simple border piece with rubout painting that you can easily and perfectly reproduce, or have reproduced, or is it a skilled piece of work, like Jesus' hand or face, where you might go to extraordinary efforts to avoid replacing the piece.

And finally, the often unpleasant decision -- especially if you must commission a more skilled painter to reproduce the piece -- what is the best repair your client can afford?

You make your decision based on all your experience and best judgement.  That's why they hired you.

[Vic Rothman]

It comes down to your judgement.  Can you make the glued piece at least match the quality of the rest of the window?  If the rest of the window has dozens of replacement pieces, or dozens of lead dutchmans, that might lead to a different decision than if the window were otherwise perfect.  Does the piece have heavy painting on it?  Can you glue the piece, fill the missing shard with Hxtal, and use a cold paint (like a non-fired enamel) to conceal the missing paint?  Is the repair going to be viewed close up at eye level, or will it be 40 feet off the ground in a busy window where no one will ever perceive it?  Is the broken piece a too-thin piece of glass right behind a rebar that will probably rebreak the next time a strong wind pushes the panel from the exterior?  Maybe you should just lead the two pieces to reduce the risk that the glued piece will break in a new place.  Does the broken piece provide structural protection/support for a more valuable piece of adjacent glass?    Perhaps you should replace it with a thicker piece to protect the more valuable piece next to it. 

Those are just some of the non-artistic considerations. Remember that large windows usually represent the work of multiple artists of different abilities.  Novice glass painters spent their hours churning out border pieces.  More experienced painters were put to work mass producing more technically challenging pieces, and the master painters painted flesh and the extremely artistically expressive and difficult pieces.  Is the piece apprentice-grade work, like a simple border piece with rubout painting that you can easily and perfectly reproduce, or have reproduced, or is it a skilled piece of work, like Jesus' hand or face, where you might go to extraordinary efforts to avoid replacing the piece.

And finally, the often unpleasant decision -- especially if you must commission a more skilled painter to reproduce the piece -- what is the best repair your client can afford?

You make your decision based on all your experience and best judgement.  That's why they hired you.

John
The purpose of conservation is to conserve what is there. If a piece of glass can be saved by gluing, then that is what is required. It is NOT up to us to decide what is worthy of conservation.  Remember it was not that long ago that you could find Tiffany windows and lamps in the town dump. Styles,trends and historic conciseness change. It's not our call as conservators.