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Bloom on leather



In a message dated 96-02-22 14:24:39 EST, MAILER-DAEMON@xxxxxxx (Mail
Delivery Subsystem) writes:

>>Subject: Re: "Bloom" on leather
>>
>>In response to the question a few days ago about the 'bloom' on certain
>>leathers: since I am the U.S. distributor for Hewit's leather tannery of
>>Edinburgh, Scotland, I took the liberty of asking them to send me some
input
>>on this subject that could be posted to the list.  Their reply is listed
>>herewith; though somewhat lengthy, I think many list members will find it
>>helpful.
>>
>>>
>>>There are two principal reasons for the development of a bloom on the
>>surface
>>>of
>>>leather - 1) microbiological agents, i.e. the growth of fungal or
bacterial
>>>colonies and 2) crystallisation of material emanating from within the
>>>leather.
>>>
>>>1) Microbial growth - this is almost always indicative of storage under
>>>inappropriate environmental conditions. Most types of leather are
>>hygroscopic
>>>and will draw in moisture from a damp atmosphere until a point is reached
>>>where
>>>micro-organisms can thrive. The visible sign of this is usually a white,
>>>powdery
>>>deposit on the surface but there is often penetration into the substrate
>>>which
>>>may not be immediately apparent. The biological processes are fuelled by
>>>digestion of the substrate resulting in an irreversible breakdown.
>>>
>>>The important remedial actions are to halt further activity by returning
>the
>>>leather to a drier state and by the use of an appropriate biocide. The
>>degree
>>>to
>>>which the original appearance can be restored is largely dependant on the
>>>nature
>>>and severity of the contamination. In many cases it will be possible to
>>>achieve
>>>a good result by brushing or lightly swabbing the surface, followed by an
>>>application of wax based penetrative leather dressing.
>>>
>>>
>>>2) Crystalline surface deposits -  known in the leather trade as "spues",
>>>arise
>>>because of the migration towards the surface of unbound, mobile components
>>>from
>>>within the leather. They are unsightly but are not, generally speaking,
>>>harmful
>>>and they often come about as a result of cyclical changes in environmental
>>>conditions, i.e. fluctuating temperature or humidity. Broadly, these
>>deposits
>>>may be subdivided into salt spues and waxy spues. The classical method of
>>>differentiating is by applying a local source of heat, for example a match
>>>flame, which will usually cause a waxy spue to melt and disappear - at
>least
>>>temporarily, whereas a salt spue will be unaffected.
>>>
>>>Salt deposits are often water soluble and can be readily swabbed away;
>>>however,
>>>as the leather dries out again further salt may be brought up to the
>surface
>>>causing a recurrence of the problem. It is important to bear in mind that
>>>soluble components are always carried towards the side where evaporation
is
>>>taking place  (this is the principle on which chromatography is based).
Wet
>>>leather should, if possible, be dried with the grain side against an
>>>impervious
>>>sheet to encourage migration away from the grain and help prevent
excessive
>>>build-up and crystallisation of salts on the grain surface.
>>>
>>>Waxy deposits are, generally, not water soluble. Localised heating , as
>>>described earlier, or polishing may be all that is required to improve the
>>>appearance but neither of these methods actually removes the surface
>>>contaminant. It  may be possible to remove this by swabbing with a weak
>>>solution
>>>of detergent or lactic acid but often it is necessary to employ an organic
>>>solvent. The same principles apply as described in the paragraph above,
>i.e.
>>>after washing off the excess, final drying should take place into the
>>leather
>>>so
>>>as to carry any residual material away from the surface.
>>>
>>>A special case exists for soap deposits which can form when certain
>metallic
>>>compounds react with oils in the leather. The types of soap most likely to
>>>cause
>>>a problem in leather are those resulting from a reaction between basic
>>>chromium
>>>or aluminium tanning agents and emulsifiable oils introduced during the
>>>leather-making process or naturally occurring free fatty acids. These
soaps
>>>are
>>>highly insoluble and may be difficult to deal with. Oxalic acid has been
>>>suggested elsewhere as a suitable material for removing soap deposits but
>>>there
>>>are two significant disadvantages to its use - firstly, it is a moderately
>>>strong acid which could lead to damage if an excess were left in the
>>leather,
>>>and secondly, it is poisonous by skin absorption and so should be handled
>>>with
>>>extreme caution. A better and safer option is to swab with iso-propyl
>>alcohol
>>>which is a fairly good solvent for many of these soaps.
>>>
>>>Aluminium and chromium soaps are not likely to be of concern to users of
>>>regular
>>>vegetable tanned bookbinding leathers. Chromium tanned leathers can be
very
>>>difficult to work with and chromium/vegetable combination tannages have
>been
>>>shown to have poor performance under accelerated aging tests. Aluminium
>>tawed
>>>and aluminium/vegetable tanned leathers, which perform very well in these
>>>test,
>>>are sold as specialist "conservation" grades, so there should be no
>>confusion
>>>as
>>>to whether or not aluminium is present. Other metals which may give rise
to
>>>soap
>>>formation include calcium and magnesium from hard water areas but the
>tanner
>>>should have taken appropriate steps to deal with any potential problem
and,
>>>in
>>>any event, these will only be present in trace quantities.
>>>
>>>It goes without saying that any methods which are to be applied to a
>leather
>>surface should be tested out first on an inconspicuous area, for example,
to
>>check for any effect on the underlying colour.  The finish film on certain
>>types of leather may be softened and rendered much more susceptible to
>damage
>>while wet, and care should be excercised in handliing the leather.  Safe
>>working practices should be adhered to when using any chemicals, this
>>includes the use of appropriate personal protective equipment and the
>>provision of adequate ventilation when using volatile solvents."
>>
>>My thanks to William McLean of J. Hewit & Sons Ltd. for this info.
>>
>>Regards, Karen Crisalli/The Bookbinder's Warehouse
>>

---------------------
Forwarded message:
From:   MAILER-DAEMON@xxxxxxx (Mail Delivery Subsystem)
To:     KarenC5071@xxxxxxx
Date: 96-02-22 14:24:39 EST

This is a MIME-encapsulated message

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The original message was received at Thu, 22 Feb 1996 14:24:38 -0500
from root@localhost

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   ----- Original message follows -----

--OAA16978.825017082/emout08.mail.aol.com
Content-Type: message/rfc822

>From KarenC5071@xxxxxxx  Thu Feb 22 22:40:41 1996
Message-ID: <"HFwb93.0.Ss4.f3FBn"@sul2>

book_arts-llist@xxxxxxxxxxxxxxxxx; Thu, 22 Feb 1996 14:24:38 -0500
Date: Thu, 22 Feb 1996 14:24:38 -0500
From: KarenC5071@xxxxxxx
Message-ID: <960222142437_228678777@xxxxxxxxxxxxxxxxxxxx>
To: book_arts-l list@xxxxxxxxxxxxxxxxx
Subject: Bloom on leather

In a message dated 96-02-22 13:59:50 EST, MAILER-DAEMON@xxxxxxx (Mail
Delivery Subsystem) writes:

>Subject: Re: "Bloom" on leather
>
>In response to the question a few days ago about the 'bloom' on certain
>leathers: since I am the U.S. distributor for Hewit's leather tannery of
>Edinburgh, Scotland, I took the liberty of asking them to send me some input
>on this subject that could be posted to the list.  Their reply is listed
>herewith; though somewhat lengthy, I think many list members will find it
>helpful.
>
>>
>>There are two principal reasons for the development of a bloom on the
>surface
>>of
>>leather - 1) microbiological agents, i.e. the growth of fungal or bacterial
>>colonies and 2) crystallisation of material emanating from within the
>>leather.
>>
>>1) Microbial growth - this is almost always indicative of storage under
>>inappropriate environmental conditions. Most types of leather are
>hygroscopic
>>and will draw in moisture from a damp atmosphere until a point is reached
>>where
>>micro-organisms can thrive. The visible sign of this is usually a white,
>>powdery
>>deposit on the surface but there is often penetration into the substrate
>>which
>>may not be immediately apparent. The biological processes are fuelled by
>>digestion of the substrate resulting in an irreversible breakdown.
>>
>>The important remedial actions are to halt further activity by returning
the
>>leather to a drier state and by the use of an appropriate biocide. The
>degree
>>to
>>which the original appearance can be restored is largely dependant on the
>>nature
>>and severity of the contamination. In many cases it will be possible to
>>achieve
>>a good result by brushing or lightly swabbing the surface, followed by an
>>application of wax based penetrative leather dressing.
>>
>>
>>2) Crystalline surface deposits -  known in the leather trade as "spues",
>>arise
>>because of the migration towards the surface of unbound, mobile components
>>from
>>within the leather. They are unsightly but are not, generally speaking,
>>harmful
>>and they often come about as a result of cyclical changes in environmental
>>conditions, i.e. fluctuating temperature or humidity. Broadly, these
>deposits
>>may be subdivided into salt spues and waxy spues. The classical method of
>>differentiating is by applying a local source of heat, for example a match
>>flame, which will usually cause a waxy spue to melt and disappear - at
least
>>temporarily, whereas a salt spue will be unaffected.
>>
>>Salt deposits are often water soluble and can be readily swabbed away;
>>however,
>>as the leather dries out again further salt may be brought up to the
surface
>>causing a recurrence of the problem. It is important to bear in mind that
>>soluble components are always carried towards the side where evaporation is
>>taking place  (this is the principle on which chromatography is based). Wet
>>leather should, if possible, be dried with the grain side against an
>>impervious
>>sheet to encourage migration away from the grain and help prevent excessive
>>build-up and crystallisation of salts on the grain surface.
>>
>>Waxy deposits are, generally, not water soluble. Localised heating , as
>>described earlier, or polishing may be all that is required to improve the
>>appearance but neither of these methods actually removes the surface
>>contaminant. It  may be possible to remove this by swabbing with a weak
>>solution
>>of detergent or lactic acid but often it is necessary to employ an organic
>>solvent. The same principles apply as described in the paragraph above,
i.e.
>>after washing off the excess, final drying should take place into the
>leather
>>so
>>as to carry any residual material away from the surface.
>>
>>A special case exists for soap deposits which can form when certain
metallic
>>compounds react with oils in the leather. The types of soap most likely to
>>cause
>>a problem in leather are those resulting from a reaction between basic
>>chromium
>>or aluminium tanning agents and emulsifiable oils introduced during the
>>leather-making process or naturally occurring free fatty acids. These soaps
>>are
>>highly insoluble and may be difficult to deal with. Oxalic acid has been
>>suggested elsewhere as a suitable material for removing soap deposits but
>>there
>>are two significant disadvantages to its use - firstly, it is a moderately
>>strong acid which could lead to damage if an excess were left in the
>leather,
>>and secondly, it is poisonous by skin absorption and so should be handled
>>with
>>extreme caution. A better and safer option is to swab with iso-propyl
>alcohol
>>which is a fairly good solvent for many of these soaps.
>>
>>Aluminium and chromium soaps are not likely to be of concern to users of
>>regular
>>vegetable tanned bookbinding leathers. Chromium tanned leathers can be very
>>difficult to work with and chromium/vegetable combination tannages have
been
>>shown to have poor performance under accelerated aging tests. Aluminium
>tawed
>>and aluminium/vegetable tanned leathers, which perform very well in these
>>test,
>>are sold as specialist "conservation" grades, so there should be no
>confusion
>>as
>>to whether or not aluminium is present. Other metals which may give rise to
>>soap
>>formation include calcium and magnesium from hard water areas but the
tanner
>>should have taken appropriate steps to deal with any potential problem and,
>>in
>>any event, these will only be present in trace quantities.
>>
>>It goes without saying that any methods which are to be applied to a
leather
>surface should be tested out first on an inconspicuous area, for example, to
>check for any effect on the underlying colour.  The finish film on certain
>types of leather may be softened and rendered much more susceptible to
damage
>while wet, and care should be excercised in handliing the leather.  Safe
>working practices should be adhered to when using any chemicals, this
>includes the use of appropriate personal protective equipment and the
>provision of adequate ventilation when using volatile solvents."
>
>My thanks to William McLean of J. Hewit & Sons Ltd. for this info.
>
>Regards, Karen Crisalli/The Bookbinder's Warehouse
>
>
>

---------------------
Forwarded message:
From:   MAILER-DAEMON@xxxxxxx (Mail Delivery Subsystem)
To:     KarenC5071@xxxxxxx
Date: 96-02-22 13:59:50 EST

This is a MIME-encapsulated message

--OAA08703.825015614/emout09.mail.aol.com

The original message was received at Thu, 22 Feb 1996 14:00:14 -0500
from root@localhost

   ----- The following addresses had delivery problems -----
Book_Arts-L@xxxxxxxxxxxxxxxxx  (unrecoverable error)

   ----- Transcript of session follows -----
550 Book_Arts-L@xxxxxxxxxxxxxxxxxxxx Host unknown (Name server:
listserve.syr.edu: host not found)

   ----- Original message follows -----

--OAA08703.825015614/emout09.mail.aol.com
Content-Type: message/rfc822

>From KarenC5071@xxxxxxx  Thu Feb 22 22:40:41 1996
Message-ID: <"cWpp73.1.Ss4.f3FBn"@sul2>

Book_Arts-L@xxxxxxxxxxxxxxxxx; Thu, 22 Feb 1996 14:00:14 -0500
Date: Thu, 22 Feb 1996 14:00:14 -0500
From: KarenC5071@xxxxxxx
Message-ID: <960222140012_150784406@xxxxxxxxxxxxxxxxxxxx>
To: Book_Arts-L@xxxxxxxxxxxxxxxxx
Subject: Re: "Bloom" on leather

In response to the question a few days ago about the 'bloom' on certain
leathers: since I am the U.S. distributor for Hewit's leather tannery of
Edinburgh, Scotland, I took the liberty of asking them to send me some input
on this subject that could be posted to the list.  Their reply is listed
herewith; though somewhat lengthy, I think many list members will find it
helpful.

>
>There are two principal reasons for the development of a bloom on the
surface
>of
>leather - 1) microbiological agents, i.e. the growth of fungal or bacterial
>colonies and 2) crystallisation of material emanating from within the
>leather.
>
>1) Microbial growth - this is almost always indicative of storage under
>inappropriate environmental conditions. Most types of leather are
hygroscopic
>and will draw in moisture from a damp atmosphere until a point is reached
>where
>micro-organisms can thrive. The visible sign of this is usually a white,
>powdery
>deposit on the surface but there is often penetration into the substrate
>which
>may not be immediately apparent. The biological processes are fuelled by
>digestion of the substrate resulting in an irreversible breakdown.
>
>The important remedial actions are to halt further activity by returning the
>leather to a drier state and by the use of an appropriate biocide. The
degree
>to
>which the original appearance can be restored is largely dependant on the
>nature
>and severity of the contamination. In many cases it will be possible to
>achieve
>a good result by brushing or lightly swabbing the surface, followed by an
>application of wax based penetrative leather dressing.
>
>
>2) Crystalline surface deposits -  known in the leather trade as "spues",
>arise
>because of the migration towards the surface of unbound, mobile components
>from
>within the leather. They are unsightly but are not, generally speaking,
>harmful
>and they often come about as a result of cyclical changes in environmental
>conditions, i.e. fluctuating temperature or humidity. Broadly, these
deposits
>may be subdivided into salt spues and waxy spues. The classical method of
>differentiating is by applying a local source of heat, for example a match
>flame, which will usually cause a waxy spue to melt and disappear - at least
>temporarily, whereas a salt spue will be unaffected.
>
>Salt deposits are often water soluble and can be readily swabbed away;
>however,
>as the leather dries out again further salt may be brought up to the surface
>causing a recurrence of the problem. It is important to bear in mind that
>soluble components are always carried towards the side where evaporation is
>taking place  (this is the principle on which chromatography is based). Wet
>leather should, if possible, be dried with the grain side against an
>impervious
>sheet to encourage migration away from the grain and help prevent excessive
>build-up and crystallisation of salts on the grain surface.
>
>Waxy deposits are, generally, not water soluble. Localised heating , as
>described earlier, or polishing may be all that is required to improve the
>appearance but neither of these methods actually removes the surface
>contaminant. It  may be possible to remove this by swabbing with a weak
>solution
>of detergent or lactic acid but often it is necessary to employ an organic
>solvent. The same principles apply as described in the paragraph above, i.e.
>after washing off the excess, final drying should take place into the
leather
>so
>as to carry any residual material away from the surface.
>
>A special case exists for soap deposits which can form when certain metallic
>compounds react with oils in the leather. The types of soap most likely to
>cause
>a problem in leather are those resulting from a reaction between basic
>chromium
>or aluminium tanning agents and emulsifiable oils introduced during the
>leather-making process or naturally occurring free fatty acids. These soaps
>are
>highly insoluble and may be difficult to deal with. Oxalic acid has been
>suggested elsewhere as a suitable material for removing soap deposits but
>there
>are two significant disadvantages to its use - firstly, it is a moderately
>strong acid which could lead to damage if an excess were left in the
leather,
>and secondly, it is poisonous by skin absorption and so should be handled
>with
>extreme caution. A better and safer option is to swab with iso-propyl
alcohol
>which is a fairly good solvent for many of these soaps.
>
>Aluminium and chromium soaps are not likely to be of concern to users of
>regular
>vegetable tanned bookbinding leathers. Chromium tanned leathers can be very
>difficult to work with and chromium/vegetable combination tannages have been
>shown to have poor performance under accelerated aging tests. Aluminium
tawed
>and aluminium/vegetable tanned leathers, which perform very well in these
>test,
>are sold as specialist "conservation" grades, so there should be no
confusion
>as
>to whether or not aluminium is present. Other metals which may give rise to
>soap
>formation include calcium and magnesium from hard water areas but the tanner
>should have taken appropriate steps to deal with any potential problem and,
>in
>any event, these will only be present in trace quantities.
>
>It goes without saying that any methods which are to be applied to a leather
surface should be tested out first on an inconspicuous area, for example, to
check for any effect on the underlying colour.  The finish film on certain
types of leather may be softened and rendered much more susceptible to damage
while wet, and care should be excercised in handliing the leather.  Safe
working practices should be adhered to when using any chemicals, this
includes the use of appropriate personal protective equipment and the
provision of adequate ventilation when using volatile solvents."

My thanks to William McLean of J. Hewit & Sons Ltd. for this info.

Regards, Karen Crisalli/The Bookbinder's Warehouse

--OAA08703.825015614/emout09.mail.aol.com--

--OAA16978.825017082/emout08.mail.aol.com--


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