SIDS

 

SIDS

Hi David,
Seems I have a little dilemma with my older works, when I started to paint.  I used hardboard for the support WITHOUT applying any gesso.   Therefore I have acrylic paints directly applied to the hardboard.  My question is in regards to some sort of final coat, should I apply medium as an isolation coat and then a varnish over this, as the process which you've taught.  My paintings these days are properly executed right down to the Golden MSA Varnish.  Also whether there will be any longevity with the acrylic onto the hardboard.  I have sold some of these early works, without any sort of finish and have another five in inventory, which I'd love to still show in hopes of selling.  Do you suggest I apply the medium and varnish front and back?  I don't feel great about selling artwork below a professional level but I do need to include these paintings in my body of work to sell. 
Denise

Hi Denise,
The problem of putting the paint, or gesso, directly on the hardboard without first sizing is that the acidic properties of the wood will migrate into the paint layers.  This can cause some brownish discoloration called SIDS (support induced discoloration) that may be visible in the light areas of the painting. I don't think it is a big factor with regards to the permanence of you work but i don't know for sure if any conservation research has been done on the long term effects.  I would varnish just like any other acrylic painting (isolation acrylic gloss medium varnish, then a layer of acrylic solution varnish like the Golden MSA).  I would put a coat of Golden GAC 700 or White Shellac on the back. 

Hi Again David,
Thank you for your reply David, the information is useful, particularly re other artists selling works in a worse state than the ones I speak of.  Nonetheless, it is precisely the professional longevity
and quality of  producing works I am interested in and your advice and knowledge base, which you generously share, is very much appreciated.  May I add that I am unclear when you refer to sizing. Is this different from gesso?  Also, the GAC 700 on the back, I had been applying the same base as the isolation coat on the face.  Is the GAC a better sealant, less costly or ?.  Thanks for your clarification on these questions.

 
Hi again Denise,
A size and a primer (acrylic gesso in this case) are different.  They serve two separate purposes.  A size is for sealing a surface to prevent physical and/or chemical interaction from happening between the gesso/painting and the support.  The hardboard is acidic and you don't want it to come in direct contact with your work so you size it, or seal the surface.   The gesso serves as a 'ground' that provides an ideal physical surface (the paint adheres well to it), and optical surface (usually white) for your painting to be applied upon.  Most paintings supports require both a size and a ground (gesso) because you rarely want your painting to be permanently affixed to a support, it makes future restoration more difficult for one thing. 

I recommended the GAC 700 as a size for the back of the panel because it is a better sealant, less absorbent that is, than the regular gloss medium that you are using for the isolation varnish -  though it is more expensive.  For the back of the panel the difference is not important however, I would use white shellac that you can purchase at the hardware store.