What is Paraloid B-72?
Paraloid B-72 (formerly called Acryloid B-72) is a stable
clear acrylic resin used in conservation as a coating, consolidant, and
adhesive. B-72 is an ethyl-methacrylate copolymer soluble in acetone, toluene,
xylene, and ethanol. Since most historic wood coatings are insoluble in
aromatic hydrocarbons, B-72 has proved to be a safe barrier coat and surface
consolidant on the majority antique furniture surfaces. Also, since the resin
is not soluble in aliphatic hydrocarbons, paste waxing over the surface is
still a viable maintenance procedure. Paraloid B-72’s thermoplasticity,
solubility parameters, and durability are the primary reasons that it has found
extensive use in conservation treatments.
Supplied Forms
B-72 can be purchased either already mixed in solution or in
clear, odorless pellet form ready to dissolve in a custom solvent blend and
concentration. I have found the latter
method easy enough for my practice. Requiring no more than a few minutes and a
few simple tools, one can easily mix their own B-72 solution. The following is
how I go about the task.
The Tools
Digital scale with 0.1 g resolution.
Small glass jar with lid
Cheese cloth
Cotton/ hemp string
Small funnel
Permanent Marker
Measuring cup measuring ml
Tap water
Desired solvent(s)
Paraloid B-72 pellets
Mixing it Up
Because we will be making a weight/volume solution, the
first task is to decide the final desired volume. For this run I have decided I
want only 100 ml of final solution. Using your measuring cup, measure out 100
ml of tap water and transfer it to the clean glass jar.
Mark the volume with a permanent marker on the side of the jar. You may discard the water and towel dry the jar. You now have a mark on your jar displaying your final volume.
Setting the jar aside, take your digital scale and weigh out
your pellets in grams. To figure the concentration percentage of the solution,
you only need to know the grams per 100 ml. If you want a 20% solution, you
will use 20 grams pellets for the final solution of 100 ml. Note that I did not
say “per 100 ml of solvent”. Weight/volume solutions are figured by adding
solids first and then “topping up” with solvent to your desired final volume.
Once you have your 20 g (for the 20% solution), take a small
square of cheesecloth and tie the pellets into a bundle with the string. You do
not want to use synthetic string for this as it may end up dissolving depending
on your solvent blend. Make sure to leave at least 6” of string for a handle
for the pouch. Drop the pellet bundle into your glass jar with the string
hanging out.
Now, using your funnel, “top up” with solvent to the permanent marker line at 100 ml. Pull the string up and screw the lid on a best as you can to allow the bundle to suspend in the solvent.
Now, using your funnel, “top up” with solvent to the permanent marker line at 100 ml. Pull the string up and screw the lid on a best as you can to allow the bundle to suspend in the solvent.
Check every hour or two. Dissolution time obviously varies greatly depending on amount of resin and the solvent choice. When the B-72 is completely dissolved, you can pull out the cheesecloth and discard. You now have your 20% Paraloid B-72 solution. Simple as that. No mess, no fuss.
The Solution Dilution
Solution
Ah, but wait… What if I want to try different concentrations
for my project? The solution for your solution dilution is found in Pearson’s
Square. Pearson’s square is a formula used to change concentrations of
solutions. It is as follows:
A Stock Solution
(%)
B New Desired
Solution (%)
C Diluent (%)
X Part of Stock
needed for New
Y Part of Diluent
needed for New
X = B – C
Y = A – B
X + Y = D
So, for example, say I took my 20% solution and wanted to
make a 5% solution out of it. In order to determine how much more solvent to
add (diluent), I plug my numbers in the formula…
A Stock Solution
(%) = 20
B New Desired
Solution (%) = 5
C Diluent (%) = 0
(There are no solids at all)
X Part of Stock
needed for New
Y Part of Diluent
needed for New
Parts of stock
solution needed: 5–0=5
Parts of Diluent
Needed: 20-5=15
So, 5 Parts stock
solution to 15 parts diluent = My 5% desired solution.
I hope this helps anyone who has wanted to try B-72. This
method can be used for any resin. I found it is much preferred to allowing the
resin to clump in the bottom and have to periodically stir it up. This
cheesecloth method really is very hands off. Any questions? Leave a comment and
I’ll get back to you.
RESOURCES
Paraloid B-72 pellets. Available from Talas 330 Morgan Ave Brooklyn, NY 11211 212-219-0770 http://talasonline.com/
The Cameo Database – “Paraloid B-72” http://cameo.mfa.org/materials/record.asp?key=2170&subkey=6848&Search=Search&MaterialName=paraloid+b72&submit.x=0&submit.y=0
