Document:

Exhibit 10.35

                               SECURITY AGREEMENT

      THIS SECURITY AGREEMENT (the "Agreement"), dated this 9th day of February,
2001, by and between Tremont Corporation,  a Delaware  Corporation  (hereinafter
called  "Pledgor"),  whose  principal  office is at 1999  Broadway,  Suite 4300,
Denver,  Colorado 80202 and NL Environmental  Management  Services,  Inc., a New
Jersey  Corporation (the "Secured Party"),  in its capacity as the holder of the
Note (as defined below).

      Section 1. Security Interest. For value received, Pledgor hereby grants to
Secured  Party,  upon the terms and  conditions  of this  Agreement,  a security
interest in and to any and all present or future rights of Pledgor in and to all
of the following  rights,  interests  and property  (all of the following  being
herein sometimes called the "Pledged Shares"):

            10,215,541 shares of NYSE-traded NL Industries, Inc. ("NL") common
        stock, par value of $1.25 per share.

As used in this  Agreement,  the  "Collateral"  shall include the Pledged Shares
together  with  any  and  all  products  and  proceeds  of the  Pledged  Shares,
including, without limitation, all dividends, cash, instruments,  subscriptions,
warrants and any other rights and options and other  property  from time to time
received,  receivable or otherwise  distributed in respect of or in exchange for
any or all of the Pledged Shares.

      Section 2. Loan Agreement.  This Agreement is being executed and delivered
pursuant to the terms,  conditions and  requirements  of that certain  revolving
note, dated as of February 9, 2001 ("Revolving Note"), pursuant to which Secured
Party has  loaned  monies  to  Tremont  Corporation  ("Tremont").  The  security
interests herein granted  ("Security  Interests")  shall secure full payment and
performance  of: (a) that certain  Revolving  Note of even date  herewith in the
principal  amount of  $13,400,000,  made by Tremont  and payable to the order of
Secured Party (such note and any notes given in modification, renewal, extension
or substitution thereof being herein sometimes  collectively  referred to as the
"Notes" and individually as the "Note"); and (b) the due and punctual observance
and performance of each and every agreement, covenant and condition on Pledgor's
part to be observed or performed  under this Agreement or the Note (all of which
debts, duties, liabilities and obligations hereinbefore described and covered by
this Agreement and the Note are hereinafter referred to as the "Obligation").

      Section 3.  Priority.  Pledgor  represents  and warrants that the Security
Interests  are  first  and  prior  security  interests  in  and  to  all  of the
Collateral, subject to the following liens thereon or security interests therein
in existence prior to the Pledgor's acquisition of the Collateral:

                                     [NONE]

      Section 4. Title to Collateral. Pledgor represents and warrants to Secured
Party that: (a) Pledgor is the owner of the Collateral; (b) no dispute, right of
offset,  counterclaim,  or defense to the Security Interests exists with respect
to all or any part of the Collateral; and (c) Pledgor will defend the Collateral
against the claims and demands of all persons other than any subordinate  claims
or liens acknowledged by Secured Party.

<PAGE>

      Section  5.  Pledgor's  Obligations.  So long as the Note is  outstanding,
Pledgor  covenants and agrees with Secured Party: (a) not to permit any material
part of the  Collateral  to be levied upon under any legal  process;  (b) not to
dispose of any of the  Collateral  without the prior written  consent of Secured
Party;  (c) to comply with all  applicable  federal,  state and local  statutes,
laws, rules and regulations,  the noncompliance with which could have a material
and  adverse  effect  on the value of the  Collateral;  and (d) to pay all taxes
accruing  after the Closing Date which  constitute,  or may  constitute,  a lien
against the  Collateral,  prior to the date when  penalties  or  interest  would
attach to such taxes;  provided,  that Pledgor may contest any such tax claim if
done diligently and in good faith.

      Section  6. Event of  Default.  As used  herein,  the term  default  shall
include any or all of the following:

            (a) The assignment,  voluntary or involuntary conveyance of legal or
      beneficial interest,  mortgage,  pledge or grant of a security interest in
      any of the Collateral; or

            (b) The  filing or  issuance  of a notice of any lien,  warrant  for
      distraint or notice of levy for taxes or assessment against the Collateral
      (except  for those which are being  contested  in good faith and for which
      adequate reserves have been created); or

            (c) Nonpayment of any installment of principal or interest under the
      Notes; or

            (d) The  adjudication  of Tremont as bankrupt,  or the taking of any
      voluntary  action by Tremont or any  involuntary  action  against  Tremont
      seeking an  adjudication  of Tremont as bankrupt,  or seeking relief by or
      against Tremont under any provision of the Bankruptcy Code; or

            (e) Pledgor  failing to comply with any other covenant  contained in
      the Notes or this Agreement; or

            (f)  Pledgor's  default  in any  payment  (regardless  of amount) of
      principal of or interest on any other indebtedness for borrowed money; or

            (g) Pledgor's  default in the observance or performance of any other
      agreement  or  condition  relating  to any  such  other  indebtedness  for
      borrowed  money or contained  in any  instrument  evidencing,  securing or
      relating  thereto or any other event shall occur or condition  exist,  the
      effect of which  default or other event or  condition  is to cause,  or to
      permit the holder of the  indebtedness to cause,  such other  indebtedness
      for borrowed money to become due prior to its stated maturity.

An "Event of  Default"  shall be deemed to have  occurred  immediately  upon any
default  described  in clause  (d) or (g) above,  if any  default  described  in
clauses  (c) or (f)  above  is not  cured  within  5  days,  and if any  default
described in clauses (a),  (b), or (e) is not cured within 30 days after written
notice from Secured Party to Pledgor.

                                       -2-

<PAGE>

      Section 7. Remedies. Upon the occurrence and during the continuation of an
Event of Default as defined herein,  in addition to any and all other rights and
remedies  which Secured Party may then have  hereunder or under the Note,  under
the Uniform Commercial Code of the State of New Jersey or of any other pertinent
jurisdiction (the "Code"),  or otherwise,  Secured Party may, at its option: (a)
reduce its claim to judgment or  foreclosure  or otherwise  enforce the Security
Interests,  in whole or in part, by any available judicial procedure;  (b) sell,
or otherwise  dispose of, at the office of Secured Party,  or elsewhere,  all or
any part of the Collateral,  and any such sale or other  disposition may be as a
unit or in parcels, by public or private proceedings,  and by way of one or more
contracts (it being agreed that the sale of any part of the Collateral shall not
exhaust the Secured  Party's  power of sale,  but sales may be made from time to
time,  and at any time,  until all of the  Collateral has been sold or until the
Obligation has been paid and performed in full);  (c) at its discretion,  retain
the Collateral in satisfaction of the Obligation  whenever the circumstances are
such that Secured  Party is entitled to do so under the Code or  otherwise;  and
(d) exercise any and all other rights, remedies and privileges he may have under
the Note and the other documents defining the Obligation.

      Section 8.  Application of Proceeds by Secured Party. Any and all proceeds
ever  received  by  Secured  Party  from any sale or  other  disposition  of the
Collateral,  or any part thereof,  or the exercise of any other remedy  pursuant
hereto  shall be applied by Secured  Party to the  Obligation  in such order and
manner  as  Secured  Party,  in  its  sole  discretion,  may  deem  appropriate,
notwithstanding  any  directions  or  instructions  to the  contrary by Pledgor;
provided that the proceeds and/or accounts shall be applied toward  satisfaction
of the Obligation.  Any proceeds  received by Secured Party under this Agreement
in excess of those  necessary  to fully and  completely  satisfy the  Obligation
shall be distributed to Pledgor.

      Section 9. Notice of Sale.  Reasonable  notification of the time and place
of any public sale of the  Collateral,  or reasonable  notification  of the time
after which any private sale or other intended  disposition of the Collateral is
to be made, shall be sent to Pledgor and to any other persons entitled under the
Code to notice;  provided,  that if any of the  Collateral  threatens to decline
speedily  in  value or is of a type  customarily  sold on a  recognized  market,
Secured Party may sell,  pledge,  assign or otherwise  dispose of the Collateral
without  notification,  advertisement  or other notice of any kind. It is agreed
that  notice  sent or given not less than ten (10)  calendar  days  prior to the
taking of the action to which the notice relates is reasonable  notification and
notice for the purposes of this paragraph.

      Section 10.  Right to Vote Collateral; Receipt of Dividends, Etc.

      (a) Unless an Event of Default shall have occurred and be continuing,  the
Pledgor shall have the right,  from time to time, to vote and to give  consents,
ratifications and waivers with respect to the Collateral,  and the Secured Party
shall, upon receiving a written request from the Pledgor, which request shall be
deemed to be a  representation  and  warranty  by the  Pledgor  that no Event of
Default has occurred and is continuing,  deliver to the Pledgor or, as specified
in such request, such proxies, powers of attorney,  consents,  ratifications and
waivers in respect of any  Collateral  which are  registered  in the name of the
Secured  Party or a nominee as shall be specified in such request and be in form
and substance satisfactory to the Secured Party.

                                       -3-

<PAGE>

      (b) If an Event of Default  shall have  occurred  and be  continuing,  all
rights of the Pledgor to exercise the voting and other  consensual  rights which
it would  otherwise  be entitled  to  exercise  pursuant to Section 10 (a) above
shall end upon five days'  notice  from the  Secured  Party to the  Pledgor  and
thereafter  the Secured  Party shall have the right to the extent  permitted  by
law,  and the  Pledgor  shall  take  all  such  action  as may be  necessary  or
appropriate  to  give  effect  to such  right,  to  vote  and to give  consents,
ratifications  and  waivers,  and take any  other  action  with  respect  to all
Collateral  with the same  force and  effect as if the  Secured  Party  were the
absolute and sole owner thereof.

      (c) Unless an Event of Default shall have occurred and be continuing,  the
Pledgor shall be entitled to receive all regular  quarterly cash dividends.  Any
other  dividends  or  distributions  or  proceeds  therefrom  on  account of the
Collateral  shall,  if  received  by the  Pledgor,  be received in trust for the
benefit of the Secured Party,  be segregated from the other property or funds of
the Pledgor,  and be forthwith  delivered to the Secured  Party as collateral in
the same form as so received (with any necessary endorsement).

      Section 11. Delivery of Notices. Any notice or demand required to be given
hereunder  shall be in  writing  and shall be deemed to have been duly given and
received, if given by hand, when a writing containing such notice is received by
the person to whom addressed or, if given by mail, two (2) business days after a
certified or registered letter containing such notice,  with postage prepaid, is
deposited in the United States mails, addressed to:

            If to Secured Party:

            NL Environmental Management Services, Inc.
            16825 Northchase Drive
            Suite 1200
            Houston TX 77060
            Attn:  Vice President and Secretary

            If to Pledgor:

            Tremont Corporation
            1999 Broadway
            Suite 4300
            Denver, Colorado 80202
            Attn:  General Counsel

Any such address may be changed from time to time by serving notice to the other
party as above  provided.  A business  day shall mean a day of the week which is
not  a  Saturday  or  Sunday  or  a  holiday   recognized  by  national  banking
associations.

      Section 12. Binding Effect.  This Agreement shall be binding upon Pledgor,
its successors and assigns, and shall inure to the benefit of Secured Party, its
heirs, successors,  assigns,  executors,  administrators,  and personal or legal
representatives.

                                       -4-

<PAGE>

      Section 13. Governing Law. This Agreement shall be construed in accordance
with and governed by the laws of the state of New Jersey.

      Section  14.  Severability.  In the  event  that  any  one or  more of the
provisions  contained  in this  Agreement  are held to be  invalid,  illegal  or
unenforceable in any respect,  such invalidity,  illegality or  unenforceability
shall not affect any other provision of this Agreement.

                                       -5-

<PAGE>

      EXECUTED as of the day and year first herein set forth.

SECURED PARTY:

NL Environmental Management Services, Inc.

By:      /s/ Robert D. Hardy
         ---------------------------------
         Robert D. Hardy

Title:   Assistant Treasurer
         ---------------------------------

PLEDGOR:

Tremont Corporation

By:      /s/ Robert E. Musgraves
         ---------------------------------
         Robert E. Musgraves

Title:   Vice President
         ---------------------------------

                                       -6-Exhibit 10.36

                                  TAX AGREEMENT
                                     between
                                 VALHI, INC.
                                       and
                             NL INDUSTRIES, INC.

      AGREEMENT dated as of January 1, 2001 by and among Valhi, Inc. ("VHI"),  a
Delaware  corporation  having its principal  executive  offices at Three Lincoln
Centre, 5430 LBJ Freeway,  Suite 1700, Dallas,  Texas 75240, Contran Corporation
("Contran"),  a Delaware  corporation having its principal  executive offices at
Three Lincoln  Centre,  5430 LBJ Freeway,  Suite 1700,  Dallas,  TX 75240 and NL
Industries, Inc. ("NL"), a New Jersey corporation having its principal executive
offices at 16825 Northchase Drive, Suite 1200, Houston, Texas 77060.

      WHEREAS,  VHI and NL are eligible to file consolidated  returns of federal
income taxes and, subject to certain jurisdictional limitations, will be subject
to combined state and local tax reporting effective January 1, 2001;

      WHEREAS, VHI and NL wish to provide for the allocation of liabilities, and
procedures  to be followed,  with respect to federal  income taxes of NL and any
subsidiaries of NL and with respect to certain combined state and local taxes on
the terms of this Agreement.

      NOW,  THEREFORE,  in consideration  of the promises and agreements  herein
contained, the parties hereto agree as follows:

      1.  Definitions.  As used in this Agreement,  the following terms have the
meanings set forth below:

            (a) Code:  The Internal  Revenue Code of 1986, as amended,  and with
      respect to any section thereof any successor provisions under such Code or
      any successor Code.

            (b) Combined  Foreign,  State and Local Taxes: For a taxable period,
      the  amount  of all  foreign,  state and local  taxes,  together  with all
      interest  and  penalties  with  respect  thereto,  for which  liability is
      computed (1) on the basis of a combined,  unitary or  consolidated  return
      (whether at the  initiative  of the tax  authority or of the taxpayer) and
      (2) by  reference  to one or more  members of the NL Group and one or more
      members of the VHI Group not included in the NL Group.

            (c) Contran  Corporation:  A Delaware corporation that is the common
      parent of a group of corporations  electing to file a consolidated federal
      income tax return.

            (d) Federal  Taxes:  All federal  income  taxes,  together  with all
      interest and penalties with respect thereto.

<PAGE>

            (e) VHI Group: VHI and those of its direct and indirect subsidiaries
      which join in the filing of a consolidated  federal income tax return with
      its common  parent,  Contran (the  "Contran Tax Group"),  as such Group is
      constituted  from time to time.  For  purposes of this  Agreement  (to the
      extent related to Combined Foreign,  State and Local Taxes), the term "VHI
      Group"  shall  include all direct and  indirect  subsidiaries  of VHI with
      reference to which Combined Foreign, State and Local Taxes are determined.

            (f) NL Group:  NL  Industries,  Inc.  and each  direct  or  indirect
      subsidiary  of NL which would be a member of an affiliated  group,  within
      the  meaning  of section  1504(a) of the Code,  of which NL was the common
      parent,  as such Group is  constituted  from time to time. For purposes of
      this Agreement (to the extent related to Combined Foreign, State and Local
      Taxes) , the  term "NL  Group"  shall  include  all  direct  and  indirect
      subsidiaries  of NL with reference to which Combined,  Foreign,  State and
      Local taxes are determined.

            (g) NL Group Tax Liability:  For a taxable period, the liability for
      Federal Taxes and Combined Foreign,  State and Local taxes, as applicable,
      that the NL Group  would have had if it were not a member of the VHI Group
      during such taxable period (or during any taxable  period prior  thereto),
      and instead filed a separate  consolidated  return for such taxable period
      (and during all prior taxable periods  beginning after December 31, 2000);
      provided,  however,  that for purposes of determining such liability for a
      taxable  period  all  tax  elections  shall  be  consistent  with  the tax
      elections made by Contran for such period. In making such tax elections it
      is understood the Contran  Corporation will make those tax elections which
      are  beneficial  to  the  Contran  Tax  Group  on  a  consolidated  basis.
      Nevertheless,  Contran  will  use its  best  efforts  in the case of those
      elections which affect the  computation of the NL Group Tax Liability,  to
      make  elections in a reasonable  manner so as to minimize the NL Group Tax
      Liability.

2.    Contran as Agent.  Contran shall be the sole agent for the NL Group in all
      matters relating to the NL Group Tax Liability. The NL Group shall not (a)
      terminate such agency or (b) without the consent of Contran,  participate,
      or  attempt to  participate,  in any  matters  related to the NL Group Tax
      Liability,  including,  but not limited to,  preparation  or filing of, or
      resolution  of  disputes,  protests  or audits with the  Internal  Revenue
      Service, state or local taxing authorities concerning, the Contran Group's
      consolidated returns of Federal Taxes, returns of Combined Foreign,  State
      and Local Taxes or the NL Group Tax Liability with respect thereto for any
      taxable  period  beginning  after  December 31,  2000.  The NL Group shall
      cooperate  fully in providing  Contran with all  information and documents
      necessary or desirable to enable Contran to perform its obligations  under
      this Section,  including  completion of Internal Revenue Service and state
      or local tax audits in  connection  with such NL Group Tax  Liability  and
      determination of the proper liability for such NL Group Tax Liability.

                                     Page 2

<PAGE>

3.       Liability for Taxes; Refunds.

            (a) VHI, as the common parent of the NL Group,  shall be responsible
      for, and shall pay to Contran or a taxing  authority,  as applicable,  the
      consolidated tax liability for the VHI Group and has the sole right to any
      refunds  received  from  Contran  or a taxing  authority,  as  applicable,
      subject to the provisions of Sections 5 and 6 of this Agreement.

            (b)  Notwithstanding  any other provision of this Agreement,  NL and
      each subsidiary of NL which is a member of the NL Group shall be severally
      liable to VHI for the NL Group Tax Liability.

            (c) NL shall  indemnify VHI and hold it and the VHI Group other than
      the NL Group, harmless from and against any deficiency in the NL Group Tax
      Liability that may be due to VHI.

            (d) VHI  shall  indemnify  NL and hold it and the NL Group  harmless
      from and against any Federal Taxes and Combined  Foreign,  State and Local
      Taxes attributable to the VHI Group or any other member of the Contran Tax
      Group,  other than the NL Group,  as such taxes are determined  under this
      and other tax sharing agreements.

      4. Tax  Returns.  VHI  shall  file on  behalf  of the NL Group any and all
federal,  foreign, state and local tax returns that are required as they pertain
to the NL Group Tax Liability. The NL Group, at VHI's request, shall join in any
applicable  consolidated  returns of Federal  Taxes and any  returns of Combined
Foreign,  State and Local  Taxes (for which  returns  have not been  theretofore
filed)  and  execute  its  consent  to each  such  filing  on any form as may be
prescribed  for such consent if such consent is required.  The decision of VHI's
Senior  Vice  President  (or any  other  officer  so  designated  by  VHI)  with
responsibility  for  tax  matters  shall,  subject  to the  provisions  of  this
Agreement, be binding in any dispute between VHI and the NL Group as to what tax
position  should be taken  with  respect  to any item or  transaction  of the NL
Group. The preceding sentence is limited to the tax positions that affect the NL
Group Tax  Liability  and the  combined  VHI Group and  Contran  Tax  Group.  In
addition,  VHI and members of the VHI Group,  including NL and members of the NL
Group,   shall  provide  each  other  with  such  cooperation,   assistance  and
information  as each of them may request of the other with respect to the filing
of any tax return,  amended return,  claim for refund or other document with any
taxing  authority.  NL shall be solely  responsible for all taxes due for the NL
Group with  respect to tax returns  filed by NL or a member of the NL Group that
are required to be filed on a separate company basis, independent of VHI.

      5. Payment of NL Group Tax Liability for Federal Taxes.  On or before each
date,  as  determined  under  section  6655  of  the  Code,  for  payment  of an
installment of estimated  Federal Taxes,  NL shall pay to VHI an amount equal to
the  installment  which  the NL Group  would  have  been  required  to pay as an
estimated  payment of Federal Taxes to the Internal  Revenue  Service if it were
filing a separate  consolidated return in respect of the NL Group Tax Liability.
Any balance owed with

                                     Page 3

<PAGE>

respect to the NL Group Tax Liability  for such taxable  period shall be paid to
VHI on or before the 15th day of the third month after the close of such taxable
period.  If it is not  possible to  determine  the amount of such  balance on or
before such day, (a) a reasonable  estimate  thereof  shall be paid on or before
such day,  (b) the  amount of such  balance  shall be finally  determined  on or
before the  earlier  of; (i) the 15th day of the ninth  month after the close of
such  taxable  period  and (ii) the date on which the  consolidated  tax  return
containing  the NL Group for such  period  is filed  with the  Internal  Revenue
Service,  and (c) any  difference  between  the  amount  so  determined  and the
estimated  amount paid shall;  (i) in the case of an  underpayment,  be promptly
paid to VHI and (ii) in the case of an  overpayment,  be  promptly  refunded  or
applied  against  the  estimated  NL Group  Tax  Liability  for the  immediately
following tax period, at the option of VHI. If the overpayment is not applied to
the  immediately  following  tax  period,  such  overpayment  shall be  promptly
refunded to the NL Group. As between the parties to this Agreement, the NL Group
shall be solely  responsible  for the NL Group Tax  Liability  and shall have no
responsibility  for Federal  Taxes of the VHI Group or the  Contran  Group other
than payment of the NL Group Tax Liability in accordance  with the terms of this
Agreement.

      6.  Refunds for NL Group  Losses and Credits  for  Federal  Taxes.  If the
calculation with respect to the NL Group Tax Liability for Federal Taxes results
in a net operating  loss ("NOL") for the current tax period that, in the absence
of a Code Section 172(b)(3) election made by Contran, is carried back under Code
Sections 172 and 1502 to a prior taxable  period or periods of the NL Group with
respect to which the NL Group  previously  made  payments to VHI,  then, in that
event,  VHI shall pay (or credit) NL an amount  equal to the tax refund to which
the NL  Group  would  have  been  entitled  had the NL  Group  filed a  separate
consolidated  federal  income tax return for such year (but not in excess of the
net aggregate  amount of the NL Group Tax Liability  paid to VHI with respect to
the preceding two taxable  periods).  If the calculation  with respect to the NL
Group Tax Liability  results in an NOL for the current tax period,  that subject
to the Code  Section  172(b)(3)  election  made by Contran,  is not carried back
under Code Sections 172 and 1502 to a prior taxable  period or periods of the NL
Group  with  respect to which NL made  payments  to VHI or is not  carried  back
because the Contran Tax Group does not have a  consolidated  net operating  loss
for the  current  tax  period,  then,  in that  event  such NOL  shall be an NOL
carryover to be used in computing the NL Group Tax Liability for future  taxable
periods,  under the law  applicable to NOL  carryovers  in general,  as such law
applies to the relevant taxable period.  Furthermore, if the NL Group would have
been entitled to a refund of Federal Taxes for any year had the NL Group filed a
separate  consolidated  federal  income  tax  return  for the loss  year and the
carryback year, VHI shall pay to NL the amount which NL would have received as a
refund from the Internal Revenue Service. Payments made pursuant to this Section
6 shall be made on the date that Contran (or any  successor  common  parent of a
tax group to which the VHI Group is a  member)  files its  consolidated  federal
income tax return for the taxable period involved.  Principles  similar to those
discussed in this Section 6 shall apply in the case of the utilization of all NL
Group loss and credit carrybacks and carryovers.

                                     Page 4

<PAGE>

      7. Payment of NL Group Tax Liability  for Foreign,  State and Local Taxes.
The  foregoing  principles  contained in Sections 5 and 6 shall apply in similar
fashion to any consolidated or combined foreign, state or other local income tax
returns,  containing  any member of the VHI Group and any member of the NL Group
that is not also a member of the VHI Group, which may be filed.

       8. Subsequent  Adjustments.  If any settlement with the Internal  Revenue
 Service,  foreign,  state or local tax  authority or court  decision  which has
 become final results in any adjustment to any item of income,  deduction,  loss
 or credit to the VHI Group in respect  of any  taxable  period  subject to this
 Agreement,  which, in any such case, affects or relates to any member of the NL
 Group as constituted  during such taxable  period,  the NL Tax Group  Liability
 shall be  redetermined to give effect to such adjustment as if it had been made
 as  part  of or  reflected  in the  original  computation  of the NL Tax  Group
 Liability and proper  adjustment of amounts paid or owing  hereunder in respect
 of such liability and allocation shall be promptly made in light thereof.

      9.  Amendments.  This  Agreement may be amended,  modified,  superseded or
cancelled,  and any of the terms, covenants, or conditions hereof may be waived,
only by a  written  instrument  specifically  referring  to this  Agreement  and
executed by both  parties  (or, in the case of a waiver,  by or on behalf of the
party waiving  compliance).  The failure of either party at any time or times to
require performance of any provision of this Agreement shall in no manner affect
the right at a later time to enforce the same.  No waiver by either party of any
condition,  or of  any  breach  of any  term  or  covenant,  contained  in  this
Agreement, in any one or more instances, shall be deemed to be or construed as a
further or continuing waiver of any such condition or breach, or a waiver of any
other condition or of any breach of any other term or covenant.

      10. Retention of Records.  VHI shall retain all tax returns,  tax reports,
related  workpapers and all schedules  (along with all documents that pertain to
any such tax returns,  reports or workpapers) that relate to a taxable period in
which the NL Group is included  in a  consolidated  or combined  tax return with
VHI. VHI shall make such  documents  available to NL at NL's request.  VHI shall
not dispose of such documents without the permission of NL.

      11.  Headings.  The  headings of this  Agreement  are for  convenience  of
reference only, and shall not in any way affect the meaning or interpretation of
this Agreement.

      12.  Governing  Law.  This  Agreement  shall be construed  and enforced in
accordance with the laws of the State of Delaware without regard to conflicts of
laws provisions.

      13. Counterparts. This Agreement may be executed in multiple counterparts,
each of which shall be an original,  but all of which shall  constitute  but one
agreement.

      14.  Successors.  This  Agreement  shall be binding  upon and inure to the
benefit of the  parties  hereto  and their  respective  subsidiaries,  and their
respective successors and assigns.

                                     Page 5

<PAGE>

      15.  Effective  Date.  This Agreement  shall be effective as of January 1,
2001.

                                     Page 6

<PAGE>

      IN WITNESS WHEREOF, the parties hereto have executed this Agreement on the
  date first above written.

                                       VALHI, INC.

                                       By:
                                                /s/ William J. Lindquist
                                                --------------------------------
                                                William J. Lindquist
                                                Senior Vice President
[Seal]

ATTEST:

                               CONTRAN CORPORATION

                                       By:
                                                /s/ William J. Lindquist
                                                --------------------------------
                                                William J. Lindquist
                                                Senior Vice President
[Seal]

ATTEST:

                               NL INDUSTRIES, INC.

                                       By:
                                                /s/ Robert D. Hardy
                                                --------------------------------
                                                Robert D. Hardy
                                                Vice President and Controller

ATTEST:

                                     Page 7

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