compo quiery:rosin-linseed oil sticky mass didnt disperse

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Lydia
Posts: 3
Joined: Wed 17 Jan, 2018 10:46 am
Location: Athens Greece
Organisation: Conservator at Bank of Greece
Interests: anything involving hand work & construction, contemporary dance, taekwondo, pilates

compo quiery:rosin-linseed oil sticky mass didnt disperse

Post by Lydia »

Hello Framers & Frame specialists
I am a conservator of works of art & antiquities based in Athens, Greece and new to the forum.
I have a quiery on compo. I am using the compo recipe I have from the gilding course at Uni (227gr pearl glue + 300ml water / 99gr finely crushed rosin +115ml linseed oil - I also have another recipe with glycerin & venice turpentin, but for this particular frame repair at work, I used the simplified version).
The above recipe has worked for me fine in the past, however this very last time I made it, I had the following problem: I mixed rosin + linseed oil and in the first 15 minutes of heating the rosin looked like it had dissolved well so I proceeded in mixing it with the glue, however upon mixing of the rosin-oil mix with the glue, the rosin became a very sticky mass which did not disperse - tried a higher temperature with continuous stiring and kind of worked but as soon as the temperature fell the material gathered again in a mass. I am wondering whether I should have insisted on the first stage of rosin-oil warming & mixing more or perhaps used a higher temperature at that same initial stage ?. Any ideas on what went wrong so I can avoid repeating the same mistake?
Thanking you in advance
Greetings from Greece
Lydia
vintage frames
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Joined: Tue 12 Jun, 2012 6:05 pm
Location: West Wales
Organisation: https://www.dermotmcardle.co.uk/
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Re: compo quiery:rosin-linseed oil sticky mass didnt dispers

Post by vintage frames »

Hi Lydia
Sorry to hear you're having problems with your compo.
The first thing that strikes me is that you are using twice the volume of water that I would use. Your glue is too weak to emulsify with the rosin.
Try mixing just 125ml water to 250gr glue, and when that is hot enough to be fully melted, then add the rosin and oil. I would also only use 60ml of linseed oil to that amount of rosin.
Do consider also using 20ml of glycerine, as that will strengthen the glue and do use the Venice Turpentine, as this will keep the compo elastic and prevent it cracking later.
Hope that will help.
Affordable Gilding Course for Professional Framers-https://www.dermotmcardle.co.uk/
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Lydia
Posts: 3
Joined: Wed 17 Jan, 2018 10:46 am
Location: Athens Greece
Organisation: Conservator at Bank of Greece
Interests: anything involving hand work & construction, contemporary dance, taekwondo, pilates

Re: compo quiery:rosin-linseed oil sticky mass didnt dispers

Post by Lydia »

Thank you very much for the prompt reply and for the advice.
I will give it a try and let you know how it went.
L.
Lydia
Posts: 3
Joined: Wed 17 Jan, 2018 10:46 am
Location: Athens Greece
Organisation: Conservator at Bank of Greece
Interests: anything involving hand work & construction, contemporary dance, taekwondo, pilates

Re: compo quiery:rosin-linseed oil sticky mass didnt dispers

Post by Lydia »

A quick follow up:
Thank you "Vintage Frames" for the useful suggestions and for helping me pinpoint the mistake I made.
The mistake was that in the first compo batch I prepared, which followed the compo recipe I had from uni, the animal glue concentration was very weak - obviously I messed up the glue / water ratio from the very beginning of the process - hence the rosin/oil did not disperse in the glue.
I followed the compo recipe that "Vintage Frames" has suggested and prepared the compo batch with glycerine & venice turpentine, but havent tried it yet on my steramould mould (I want to replicate a missing deco element from a compo frame I am conserving). When kneading it in gesso I found it much more elastic / plastic compared to the compo recipe I have used in the past (which was somewhat more "dry" but took uo good detail from moulds) - so now I just want to see how much detail the new compo will take up from the mould.
Thinking of the addition of glycerine in the hide glue and what that means physicochemically for the resulting glue properties, I thought I'd share with any of you interested in animal glues , an article on their properties:
http://www.tandfonline.com/doi/abs/10.1 ... ement-1.55
You can copy the DOI and put it on sci-hub to get the full article , alternatively if you cant find it, just let me know and I will email it to you.
In conservation we avoid adding plastisicers when preparing animal glues to be used for consolidation of works of art. Maybe thats why the compo recipe I had from uni did not involve glycerine or venice turpentine.
All this also made me think how useful theme professional development workshops are, and by this I mean workshops-seminars where specialists can exchange practical & theoretical info and keep up with changes in practices in their profession.
Thank you again for the help.
Lydia
vintage frames
Posts: 1349
Joined: Tue 12 Jun, 2012 6:05 pm
Location: West Wales
Organisation: https://www.dermotmcardle.co.uk/
Interests: Making picture frames
Contact:

Re: compo quiery:rosin-linseed oil sticky mass didnt dispers

Post by vintage frames »

Good to hear you're having a bit more fun with your compo.
I've always found that there is a "sweet spot" temperature for the compo to give the best casting detail. God knows what it is in actual degrees but if you let the compo cool a bit inside the mould before pressing, you tend to get the best detail. Giving it two squeezes can help as well.
I shouldn't be too precious about adding glycerine to the hide glue. It gives the glue the property of retaining a small degree of water so that it doesn't dry out, become brittle and crumble. And it's a natural product. The Venice turpentine does something the same for the rosin by keeping it elastic and not cracking. Cracking and overdrying of the glue will cause the compo to fail and fall away from the item you're trying to conserve.
So let us know how you get on.
Affordable Gilding Course for Professional Framers-https://www.dermotmcardle.co.uk/
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